Why do people tell the prefixes they find? Do they collect each prefix. Which prefix are the most expensive or rare. If they are rare why are they hard to find. Does this increase there value.
Oh by the way. Is there a new signature on the five dollar bill>
Cheers. 
Hi there- yes the prefixes are often subsets of notes. Like, someone might want to collect a whole series - which would include all prefixes, like APA to APZ (just an example).
Sometimes, for whatever reason, the printers cut some runs short, so that makes it very exciting when you find out you have one that is rare (and often times we don't know ffor sure until long after the notes are unavailable. Months anyways at times.
Lots of fun to track too :-)
