Agree with most of what you say.
I struggle with the point about the LSE allowing this to list on "fresh air". can you prove that? I can't.
I don't believe the initial contracts existed...that they were ever sold or that the payments existed but I have no proof of that and it could be I am wrong. I stick to the view that unless we know what the process was that was followed to carry out the fraud we don't know where it happened. IMHO we need this info to find out at what stage exercising a specific duty would have found it out and hence who failed. Hunting the LSE on the basis of "Well it went wrong didn't it" may have a moral attraction but I don't see it getting very far without some ammunition to put in the gun.
On a very practical point, if the facts aren't known, the LSE would be bound to mount a vigorous (expensive) defence and the LAG will have to fund a response.