here's some useful info i found for ya:
QUOTE
• A banknote specimen is a real (original) note which is used only for demonstration and to be distributed to banks to know the note before it is issued in the market.
• Any Central Bank, before issuing a certain note, takes a small quantity to be sent to other Central Banks around the globe. To avoid its use as a legal tender note, it can be perforated, punched, without a serial number or a serial of 000000 (all zeroes), overprinted with the word "Specimen" or "Cancelled" in any language.
• Most central banks are conservative about printing and distributing the specimen and specimens are distributed mostly between central banks.
• The quantity is small and distribution is limited so a specimen note is very special. In many cases specimens are more expensive than issued notes.
• Some countries produce more quantities of specimen notes and sell them to collectors such as Bahrain's full set and it has a serial number preceeded by the Maltese cross. So that makes its value slightly less than the original specimen.