Got two sheets issued in 1980. I am showing only the one with the following overprinted text:
Magyar-Csehszlovak-Iengyel
Csucstalalkozo
Visegrad 1991 II 15

Not knowing Hungarian Language, I understand that the sheet without overprinted text is related with Bibliotheca Corviniana.
Then the sheet was overprinted.
Is this sheet (or both) listed somewhere?
Any more info I can get? Is there a philatelic value in it? Or is just a Cinderella?
Thanks, Virgil