grodog
Hero
Bullgrit: to some degree, I think you may be seeing a generation gap among the grognards with the c. 1981 cut off date. Many old-school folks began to play D&D with the release of the Moldvay Basic/Cook Expert sets with the Erol Otus inter-linked covers (1981) for example; others, however, began quite a bit earlier, perhaps before modules were being published at all. So, all of these folks share the common grognard experience of playing the classic modules, but there will be some skew toward those earlier modules in part because they're the ones that were first available (as monochrome covers in the late '70s), and also because those exact same modules were reprinted by TSR in new color-cover collected editions starting in 1981, to draw in the newer players.
A second point to consider hiding in behind your stats is module length, I think. Here are some stats on TSR's module page lengths through 1983, listing modules by page count then within a single count, alphabetically:
1978
- G1: 8 pages
- G2: 8 pages
- S1: 12 pages (20 more in illustration booklet; 1981 green version same page counts)
- G3: 16 pages
- D1: 16 pages
- D2: 20 pages
- D3: 32 pages
1979
- S2: 12 pages
- T1: 24 pages (16 pages of module, 8 pages of maps; 1981 light green = same)
- B1: 32 pages
1980
- C2 red: 20 pages
- A1: 24 pages
- B2: 28 pages
- X1 blue: 30 pages
- C1: 32 pages, 8 more page illos booklet
- Q1: 32 pages
- S3: 32 pages with 36 page illos booklet
1981
- S1 green: 12 pages (20 more for illustration booklet)
- S2 orange: 16 pages
- T1 light green: 24 pages
- A3: 28 pages
- A4: 28 pages
- D1-2 blue: 28 pages
- D3 blue: 28 pages
- I1: 28 pages
- L1: 28 pages
- X2: 28 pages
- B1 brown: 32 pages
- B3 orange and green: 32 pages
- G1-3 green: 32 pages
- U1: 32 pages
- A2: 40 pages
1982
- B4: 28 pages
- N1: 28 pages
- C1 brown: 32 pages, 8 page illos booklet
- I2: 32 pages
- I3: 32 pages
- U2: 32 pages
- S4: 32 pages (2 booklets, each 32 pages; adventure is only in booklet 1 though)
- WG4: 32 pages
- X3: 32 pages
1983
- O1: 16 pages (2 booklets, each 16 pages)
- B5: 32 pages
- EX1: 32 pages
- EX2: 32 pages
- I4: 32 pages
- I5: 32 pages
- I6: 32 pages
- L2: 32 pages
- M1: 32 pages
- M2: 32 pages
- UK1: 32 pages
- UK2: 32 pages
- X1 red: 32 pages
- X4: 32 pages
- X5: 32 pages
- U3: 48 pages
These then average out to:
1978: 16 pages
1979: 16.8 pages
1980: 26.86 pages
1981: 27.73 pages
1982: 31.11 pages
1983: 32 pages
So, you're looking at an age demographic that strongly prefers smaller modules, I think, too. I think that preference is part of why T1 fares better than L1, for example. (And, FWIW, the era of the 8, 12, 16, and 20 page module really only lasted for two years of TSR's production---1978 and 1979---and even then, longer modules balanced out the shorter ones to bump the average count to 16 pages).
A second point to consider hiding in behind your stats is module length, I think. Here are some stats on TSR's module page lengths through 1983, listing modules by page count then within a single count, alphabetically:
1978
- G1: 8 pages
- G2: 8 pages
- S1: 12 pages (20 more in illustration booklet; 1981 green version same page counts)
- G3: 16 pages
- D1: 16 pages
- D2: 20 pages
- D3: 32 pages
1979
- S2: 12 pages
- T1: 24 pages (16 pages of module, 8 pages of maps; 1981 light green = same)
- B1: 32 pages
1980
- C2 red: 20 pages
- A1: 24 pages
- B2: 28 pages
- X1 blue: 30 pages
- C1: 32 pages, 8 more page illos booklet
- Q1: 32 pages
- S3: 32 pages with 36 page illos booklet
1981
- S1 green: 12 pages (20 more for illustration booklet)
- S2 orange: 16 pages
- T1 light green: 24 pages
- A3: 28 pages
- A4: 28 pages
- D1-2 blue: 28 pages
- D3 blue: 28 pages
- I1: 28 pages
- L1: 28 pages
- X2: 28 pages
- B1 brown: 32 pages
- B3 orange and green: 32 pages
- G1-3 green: 32 pages
- U1: 32 pages
- A2: 40 pages
1982
- B4: 28 pages
- N1: 28 pages
- C1 brown: 32 pages, 8 page illos booklet
- I2: 32 pages
- I3: 32 pages
- U2: 32 pages
- S4: 32 pages (2 booklets, each 32 pages; adventure is only in booklet 1 though)
- WG4: 32 pages
- X3: 32 pages
1983
- O1: 16 pages (2 booklets, each 16 pages)
- B5: 32 pages
- EX1: 32 pages
- EX2: 32 pages
- I4: 32 pages
- I5: 32 pages
- I6: 32 pages
- L2: 32 pages
- M1: 32 pages
- M2: 32 pages
- UK1: 32 pages
- UK2: 32 pages
- X1 red: 32 pages
- X4: 32 pages
- X5: 32 pages
- U3: 48 pages
These then average out to:
1978: 16 pages
1979: 16.8 pages
1980: 26.86 pages
1981: 27.73 pages
1982: 31.11 pages
1983: 32 pages
So, you're looking at an age demographic that strongly prefers smaller modules, I think, too. I think that preference is part of why T1 fares better than L1, for example. (And, FWIW, the era of the 8, 12, 16, and 20 page module really only lasted for two years of TSR's production---1978 and 1979---and even then, longer modules balanced out the shorter ones to bump the average count to 16 pages).