Unfortunately, the BEP's records of serial numbering for many older series are lost or incomplete. Other data of interest, such as the serial ranges for various groups of mismatched-serial or inverted-character error notes, were of course never known or recorded by the BEP.
However, in some cases, it is possible to reconstruct the lost serialling information by combining our knowledge of print run sizes and numbering practices with our observations of the serial numbers of notes known to exist. More often than not, such reconstruction requires a substantial number of data points to work from, and this is where the surveys come in.
The surveys linked below represent attempts to gather information on existing notes in certain serial ranges. Each survey page explains in more detail (a) what notes are being sought, (b) what information about these notes is needed, and (c) what I hope to learn by compiling this information. If you happen to have any notes that match what I'm looking for, please do let me know. Many thanks!