Well, apart from asking at Les Ambassadeurs, the family representative and somebody asking at EON for me where else would you suggest I should be asking?
Yes, I would assume that props would be logged in and out at a film company as you say (if they were just used as a prop) but casino plaques? In the 1960s? Doubtful. They may have had something written down at the time that stated how many were sent but unless they used the first numbers (as an example) so that they knew the ones coming back were real and checked against a list, it is doubtful that is was that minute in detail.
I thought that the cash desk may be able to help but no chance, finding records from that long ago and with the amount of different owners they have had I expect there isn't any Le Cercle paperwork anywhere to be found. And even if there was, finding somebody who would actually care enough to be bothered to look would be almost impossible. And there certainly aren't any people who worked there then still there now.
Yes, you may have had luck in other situations (Stakis etc etc etc) asking about casino items but finding out about plaques that were sent to a film company 60 years ago is a bit of a stretch and would involve questions that would likely be irrelevant to a casino manager/owner.
Plus hardly anybody who may be able to shed light on which serials were used is still breathing and even if they were I doubt they'd remember something as trivial as that even if they had been close enough to see the numbers.
The changeur may have had a sneaky look as he was an actual casino person who worked for Aspinalls but he's long gone. He may well have told people for years about his role in the film but I doubt he mentioned serials as it would take away the effect of the story which would have likely been all about his experience, who he met or spoke to and the like.
The family are a no go area but again, I doubt that they know the answers either but I did ask the person connected to them.
So basically I've tried the only avenues open to me and didn't get anywhere and I did know where to ask but hey..................