The original Reverso 1931 came in 2 versions, including the 'deluxe' one which was one of the first watches at the time to be fitted with a Sahire glass.
(standard was organic acrylic + unadjusted movement, deluxe was saphire and 15 jewels adjusted mvt).
I don't know where you have seen that the tribute is plexy, but I believe this is not the case, and a saphire in the tribute is very consistent with the original 'dleuxe' reverso.