Bill - and Andy B,
It is likely that, with the passing of 80 years already, we'll never know anything for sure. But just to add to the conundrum, I've just been looking at a photo of a TTR with a 4 spring clutch! (It's in a weird format and won't attach here).
Meanwhile, I took this photo of alleged A parts which just goes to show the massive availability of Burman parts over the years - essentially the same but, in many cases, different enough not to fit! Starting at 12 o'clock, is a NOS slotted clutch basket with slots 1/4 wide and 1-5/16 long. But I have another (not shown) with 1" long slots. At 1 o'clock is the metal shroud that goes over the basket. Then there is the (5 spring) clutch centre that stands 1.5" high (this might be a C Comet one?) and below it, the one that stands 1-1/4" high! Next, is how the back of an A clutch should look; and alongside it (at 7 o'clock) is my TTC clutch (4 spring) with one of the original thin tin-plate pressure discs - with adjustment facility. At 9 o'clock is another tin-plate disc - but undrilled and having no adjustment facility! And finally at 11 o-clock is the later Burman pressure-plate (some have adjustment, some not).
Always use this one on a Series A 5-spring clutch, or beef-up the tinplate one with more layers of welded-on tinplate (on the inside) for the 4-spring clutch; why? because it warps badly in use and causes all manner of problems!
The first of Bill's links is about 33%
not relevant to Series A machines - so expect to get even more confused if you study it closely! The second link (the 1926-35 one) is a good likeness of the early 4-spring Series A clutch; and not far off the later 5-spring variant.
I'm not even going to mention the 7" A Twin clutch....!!!
Peter B