Some of those pre-security notes did not have their position pairs included in the algorithms of the SNDB because when the SNDB was created those position pairs were not well documented (and I believe still are not to this day). It's not quite as simple as just knowing what the position pairs are - part of it includes what range of notes those position pairs will be found on. That said, I no longer maintain the SNDB and have no control over it. Pre-security notes are encountered infrequently enough that not being able to add some of them to the SNDB doesn't make much difference. My suggestion would be to just disregard it and carry on with your day. Cheers!
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.