Identifying Austin Sevens by their Factory Initials

[JonE]

Sadly we can't apply rationality! If one looks at the Production Changes book, I can see that Dave Martin has interpreted where possible but in other places, one can perhaps only state facts. And the cards may not have been the only source (we once had.)
The P/PA thing seems to be the same as D/AD (or Ad initially) i.e. P was the start, but what other could 1929 be other than long scuttle?
PB has 27.5" bonnet, PC 25.5"bonnet... so following the development elsewhere. Both short scuttle.
Perhaps he could be approached on PL and PF and whether there are extant cars or whether they are like the RF (1) variant, recorded but probably lost?