Among other things (which I will leave for other members to mention), plate numbers help establish a chronology. For example, with the 1954 $1 notes, CBN started printing with plate #1 on the A/A prefix. As time went on, the prefixes incremented, as did the plate numbers. I have a note from the X/O prefix with plate numbers 115/115. If you found a note without any serial numbers, printed by CBN, and with Beattie/Rasminsky signatures, you could look at the plate numbers for information on when it might have been printed. A lower number would indicate that it may have had a denominational letter of L. A higher number might indicate O.
Logged
BWJM, F.O.N.A.
Life Member of CPMS, RCNA, ONA, ANA, IBNS, WCS.
President, IBNS Ontario Chapter.
Treasurer, Waterloo Coin Society.
Show Chair, Cambridge Coin Show.
Fellow of the Ontario Numismatic Association.