Pyrex Collector Forums

I have a Gaiety pattern casserole dish in good condition that has a backwards backstamp (ie. XERYP) - I've had an enquiry about selling it already but have no idea if this unusual stamp adds value as its so rare? Has anyone come across a backwards stamp in this era of opalware? I know some 1920s pieces do because if the clear mounds being used but I cannot find any info on this happening with 50s or 60s pieces.

Can't speak to UK Pyrex, but do know of Delphite blue Pyrex pieces made from molds for primarily clear pieces like pie plates which are mistaken for reversed backstamps, but which were in reality made to be read from the top/inside. Stan at thatretropiece.com may have more knowledge of your dish than I.