Fakes, Clones And Certificates

The red stamp has a Gilbert (Prof. Rudolf Gilbert) signature, a well known (old time) stamp examiner. This signature is known to have been faked rather often so this stamp requires a new certificate. Why some idiot printed "smooth paper" along the bottom edge is anyone's guess, it was certainly not Gilbert. There is another signature at bottom right I don't recognise (probably of the idiot?).

I am still on vacation , when I get back home I would like to look at this issue .

This could be a Austrian specialist or even a Czech specialist who learned of a different type of paper used to print the stamp . They then marked the rear of the stamp . This discovery was made years if not decades later after the stamp was marked by the expert . Not ready to call anybody a idiot until more research done on the underlining stamp .

So at this time is it a forgery or did two different experts mark the stamp ,so is one of them wrong or both are wrong with the marking not sure

The signature Gilbert on your red stamp stands for:
Mint stamp, with overprint, genuine

The examiner symbol at bottom right would mean exactly the same for a USED stamp if the symbol read from bottom right to top right

The mark at bottom right appears a monogram capital T either over or behind a capital M, oriented horizontally. It might be in the same colour ink as the 'hladky papir' mark.