IMO you cannot safely extrapolate from the "wanted" posters that you own that all posters from the period will not glow. There has always been many different paper stocks in commercial print, each manufactured for a particular print application and reproduction process, for example you would not print an artprint on newsprint - they require a completely different stock.
I am surprised to learn that an auction house would be able to perform an analysis of the ink in-house because firstly you have to be able to identify the ink manufacturer and the manufacturing information such as the first date of production. Secondly, one then needs previous lab data on the identified ink that involves the examination of the aging of the ink such as the evaporation of ink solvents and the degradation of dyes, in order to establish when the ink was applied.
Even halftone screen characteristics and profiles from the 1930s to the 1980s would be extremely difficult to differentiate without the screen manufacturers data to draw upon. Film screens have pretty much dissapeared with the advent of modern Digital Mezzotint B and precision schoastic screening used today so this would at least be an indicator for modern printing but the 1930's to 1980's would be very difficult IMO without specialist forensic expertise with halftone screen profiles.
In the future even modern screen types will undoubtably present identification problems when you have:
Original Digital Mezzotint
Original Stochastic Screens
Digital Mezzotint - Variant B
Precision Stochastic Screens
Regardless of the above, very good luck in getting a prompt and full refund.
Out of interest, do you have any images of a period example "wanted" poster from your collection and the fake poster you bought?