It is a commemmorative "note" printed by Thomas De La Rue for the 40th anniversary of the International Bank Note Society. It was not issued by any country and does not have a face value. You will not find it in a catalog. It was given to IBNS members in 2001.
It is not really 50 anything although the "denomination" identified on the note is 50 core. The note is simply a sample note produced by De La Rue for their portfilio that they send to potential customers. It was overprinted by TDLR for IBNS with the anniversary logo at their request to make a souvenir. The note was not specially commissioned, TDLR used a note they had readily available. If they had a 40 "something" note readily available at the time, I am sure that it would have been used.
