The regular issues of 1927-36 provide a rich field of study and have not been fully researched.

I have started to do some study and find that the issues exist on a variety of papers and several different gums can be found. I note the following gums - white, gray, yellow and brown.
I have found the following papers:
Thin, white, horizontal mesh
Thin, white, vertical mesh
Thin, yellow, horizontal mesh
Medium, white, indistinct mesh
Medium, gray-white, indistinct mesh
Medium, yellow, indistinct mesh
Medium, yellow, soft, distinct vertical mesh
Medium, yellow, soft, distinct horizontal mesh
Thick, white, soft, vertical mesh
Thick, white, soft, indistinct mesh
Thick, yellow, soft, horizontal mesh
Thick, yellow, soft, indistinct mesh

Essays and Proofs exist for this issue. A number of years ago Brian Moorhouse published an offering and the following is taken from that listing as well as the information in Kneitschel.

The 1c, 2c, 7c, 10c, 20c and 70c as well as the 1P, 2.50P, 3P, 5P, 10P and 20P original lithographic artwork for sheets of 50 stamps exist. Also in existence is a composite die proof in black on paper comprising 8 copies of the 70c and 8 copies of the 1.50P.

Further plate proofs exist for the following:

1c - on thick glossy card in green; on thin card in green

2c - on thick glossy card in green, blue; on thin card also in green as well as blue

7c - on thick glossy card in green, blue; on thin card also in green as well as blue

10c - on thick glossy card in brown-carmine; same color on thin card

20c - on thick glossy card in brown-carmine; on thin card in brown-carmine, red-violet

50c - on thin card in gray-lilac and turquoise green

70c - on thick glossy card in violet-brown; on thin card in red carmine this latter known in a block of 25

1P - on thick glossy card in deep blue green; on thin card in pale green

1.5P - on thick glossy card in yellow-bistre, brown; on thin card in yellow-bistre as well as gray-brown

2.50P - on thick glossy card in blue, brown; on thin card in coffee or blue

3P - on thick glossy card in blue or brown-carmine; on thin card in brown-carmine

5P - on thick glossy card in chocolate

10P - on thin card in black, deep brown, and lake brown.

20P - on thick glossy card in brown lilac; on thin card in the same color.

The standard perforation for all values is 12. I have not been able to find much information on dates of issue other than the year. All values were produced by the Government Printing Works either by means of lithography or typography. The sheet size appears to have been 50 although with interpanneau pairs known, this may have been the post office sheet size while the printed sheet was one of 100.

Issued in 1931, printed by lithography with the following varieties known: Perf 11 1/2, interpanneau pair (vertical)

Issued in 1930, printed by lithography with the following varieties known: Perf 11 1/2, interpanneau pair (vertical)

Issued in 1927, printed by typography with the following varieties known: Perf 11 1/2, watermarked Gloria Bond

Issued in 1929, printed by lithography and the only variety reported is the 11 1/2 perf.

Issued in 1928, printed by typography with the following varieties: watermarked Gloria Bond, perf 11 1/2 watermarked Gloria Bond. (I suspect the unwatermarked perf 11 1/2 also exists)

Issued in 1931, printed by lithography with the following varieties: Perf 11 1/2; Imperf pair (w/o gum)

Issued in 1930, printed by lithography with the only variety being perf 11 1/2.

Issued in 1935, printed by lithography. The following varieties are known: pair, imperf horizontally; pair, imperf vertically; perf 11 1/2, perf 11 1/2, pair imperf vertically;perf 11 1/2, pair, imperf horizontally;perf 11; perf 11, pair, imperf horizontally; perf 11, pair, imperf vertically; perf 11 x 12; perf 10 1/2;imperf pair.

Issued in 1928, printed by typography with the following varieties: perf 11 1/2; watermarked Gloria Bond

Issued in 1930, printed by lithography. The only variety I have recorded is perf 11 1/2

Issued in 1931, printed by lithography. The varieties are: perf 11 1/2 and imperf pair (w/o gum)

Issued in 1935,lithographed. I note the following varieties: pair, imperf horizontally; pair, imperf vertically; perf 11 1/2; perf 11; perf 11, pair, imperf horizontally; perf 11, pair, imperf vertically; perf 11 x 12; perf 10 1/2; imperf pair

Issued in 1927, typographed. I record the following varieties: watermarked Vencedor Bond; pair, imperf horizontally; pair, imperf horizontally watermarked Vencedor Bond; watermarked Indian Bond; watermarked Adbance; strong offset on back.

This value has several distinct shades including a pale red, a scarlet (first of the shades) and pink (issued in September 1929.) The printing is typography and I show the following varieties: watermarked Gloria Bond; pair, imperf horizontally; pair, imperf vertically; perf 11 1/2; perf 11 1/2, watermarked Gloria Bond; perf 11; perf 11, pair, imperf horizontally; perf 11, pair, imperf vertically; perf 11 x 12; perf 10 1/2 x 11 1/2; imperf pair; imperf pair watermarked Gloria Bond; watermarked Vencedor Bond.

Issued in 1930, lithographed. The only variety is the perf 11 1/2

Issued in 1931, lithographed. The only variety I note is an imperf pair (w/o gum)

Issued in 1934, lithographed. I do not record any varieties of this stamp.

Issued in 1936, lithographed. Not noted in Kneitschel, but listed in Scott and Gibbons. I record the following varieties: Perf 11 1/2; perf 11; perf 10 1/2 x 11 1/2; strong offset on back

Issued in 1928, typographed. This stamp has the following varieties: watermarked Gloria Bond; pair, imperf horizontally; pair, imperf horizontally, watermarked Gloria Bond; pair, imperf vertically; pair, imperf vertically, watermarked Gloria Bond; perf 11 1/2; perf 11 1/2, watermarked Gloria Bond; perf 11; perf 11, watermarked Gloria Bond; perf 11, pair, imperf horizontally; perf 11, pair imperf horizontally, watermarked Gloria Bond; perf 11, pair, imperf vertically; perf 11, pair, imperf vertically, watermarked Gloria Bond; perf 11 x 12; perf 11 x 12, watermarked Gloria Bond; imperf pair; imperf pair, watermarked Gloria Bond; perf 11, interpanneau pair, imperf horizontally

Issued in 1927, typographed. I record the following: watermarked Gloria Bond; watermarked Vencedor Bond; strong offset
on back

Issued in 1930, lithographed. The following varieties are known to me: perf 11, pair, imperf horizontally; perf 11 1/2 watermarked Gloria Bond

Issued in 1934, lithographed. The only variety I know is the pair, imperf vertically.
This stamp was reprinted in 1936 by typography and exists in the following varieties: pair, imperf horizontally; pair, imperf vertically; perf 11 1/2; perf 11; perf 11, pair, imperf horizontally; perf 11, pair, imperf vertically; perf 11 x 12;imperf pair

This was first recorded in the IBJ (Illustriertes Briefmarken Journal) in the 15 October 1927 issue. It is typographed and exists in the following varieties: watermarked Gloria Bond; watermarked Vencedor Bond; imperf pair; imperf pair, watermarked Vencedor Bond; pair, imperf horizontally; strong offset on back

First mentioned in the IBJ issue of October 15, 1932, although listed in all catalogs as being issued in 1928. It is typographed and the only variety is the watermarked Gloria Bond one.

Issued in 1932, lithographed, no known varieties

Issued in 1937, typographed, known with a GLoria Bond watermark

Issued in 1927, typographed, with the following varieties: watermarked Gloria Bond; watermarked Vencedor Bond; strong offset on back

Issued in 1936, typographed. The only variety I know of is perf 11

Issued in 1936, typographed. The following varieties are known: pair, imperf horizontally; pair, imperf vertically; perf 11 1/2; perf 11, pair, imperf horizontally; perf 11, pair, imperf vertically; perf 11 x 12; imperf pair

Issued in 1927, typographed. The following varieties are known: watermarked Gloria Bond; imperf pair; imperf pair, watermarked Gloria Bond; perf 11 1/2; perf 11 1/2, watermarked Gloria Bond; watermarked Vencedor Bond

Issued in 1936, typographed. No varieties reported.

Issued in 1938, typographed. The following are the varieties I have recorded: pair, imperf vertically; perf 11 1/2; perf 11 1/2, pair imperf horizontally; perf 11

Issued in 1928 and although listed separately by Scott is a part of the series and is so listed by Gibbons and Kneitschel. The following are the varieties: watermarked Indian Bond; imperf pair; imperf pair, watermarked Indian Bond

Issued in 1928. The following varieties are known: watermarked Indian Bond; imperf pair; imperf pair, watermarked Indian Bond

Issued in 1928 and no varieties have been reported

Issued in 1929, typographed. The following are the varieties: watermarked Indian Bond; imperf pair; imperf pair, watermarked Indian Bond. 10,000 were issued

First noted in the philatelic literature on 15 December 1929, all catalogs show it as being issued in 1929. It is typographed and has the following varieties: watermarked Indian Bond; imperf pair; imperf pair, watermarked Indian Bond. 10,000 were issued.

Listed in catalogs are being issued in 1929, it too was first mentioned as being issued in the 15 December Issue of the IBJ. It is typographed with the following varieties: watermarked Indian Bond; imperf pair; imperf pair, watermarked Indian Bond. 10,000 were issued.