Hello Numistas!
Just wondering, because the “certificate” is an actual banknote with an overprint stamp. I'm specifically speaking about N# 356435, N# 403201 and N# 316631.
For that matter, N# 203957, appearing under China, which is a Japanese 10 yen with red overprints, should also be considered exonumia.
Again, just wondering...
Cheers!
FanDeLaU