some questions

When I worked in university, I came across the saying 'if you want to know if you really understand a subject, try teaching it'. In a similar way, whilst compiling these notes on LNER instruments has demonstrated the information which can be gleaned from study of old block instruments and their wiring diagrams, it has also highlighted some gaps in that information.

So here are some issues to ponder:

Thompson instruments
Were the Thompson blocks the first example of Welwyn control? It seems probable.
Were the Thompson blocks developed specifically to provide Welwyn control (possible), or were they modified from something else, in order to provide it?
Why do they all seem to have originally had a plunger, yet most were modified by replacement with a tapper? If the plungers caused problems, why did they keep on fitting them? An example: my block from Welwyn Garden City has the later circuit (1B), yet was still originally fitted with a plunger.

evolution of block control circuits
Are there any examples of 'drop handle' blocks with the ratchet contact? (circuit 1A) - I've not found any.
The most common examples of Welwyn control blocks which turn up are the 'drop handle' variety with the 'back box' (circuit 1B). Given that this is the later circuit, are all these 'back box modifications' BR, rather than LNER? Do photographs of block instruments in-situ in signal boxes shed light on this issue?

date of manufacture of 'Black Box' instruments
Some people have referred to these as wartime or austerity instruments, I note that date on the wiring diagram (1945) is consistent with this.

hybrid circuit 1+2 - drop handle blocks modified for use with BZR unit
What was the reason for the development of these blocks, and in particular, the retention of contacts A B X and Y?

Welwyn release
Was the standard rectangular release, with both N and R contacts and the handle on the side, the original form of this device?