The "Elstree Project" you're referring to is a later recast of the ESB-MC (mine). Provided RS's claims are legit and they didn't get duped into a 2nd Gen helmet, that makes a total of two 2nd Gen casts available. Mine, and theirs.
It almost looks as if the later generation recasts have directly influenced these earlier generation casts becoming available. Whatever the case may be, I think that early generation ESB casts for the wider audience is good for Fett fans. You have to wonder if these will now lessen the relevance of the later gen recasts; I would certainly think so as the goal is always likely to be to get as close to the source as possible. As he points out in the video, the more generations you introduce the more distortions and shrinkage you're likely to get so 2nd gen is going to be more desirable than a later generation,well, at least in my view.
This is certainly cool on all angles...but, the current EFX Fett, which I also have, was made from a cast directly off the screen used ESB helm?
Or are they talking about just a straight, unaltered casting?