Q. what is a REplacement Note

A.
When an imperfect- damanged note is detected during the manufacturing process after the serial number has been overprinted, it must be replaced with a new note.
A replacement note is used to replace the imperfect note. The prefix is usually replaced with a special prefix, such as an asterisk, star, letter or a similar device.
These are naturally scarcer than the regular note and usually command a premium from 2 to 6 times, you may also see replacement notes(non- USA) selling for 10 times over the price for the regular note. It all depends on the Country the note is from, the availability and naturally the demand.