I am always happy to help fellow collectors find the info they're after. Most often, when I do go down certain Internet goose-chases, I usually learn more about the topics that interest others. It's all good.
I had no idea that some collectors collected by
FPN &
BPN combos until I read @ChadCoins thread about the 1867-1967 Centennial ONES!
One thing that did interest me about the
FPN &
BPN combos was that for a very brief interlude, the
CBN &
BABN printers experimented my omitting the
FPN on certain prefixes of the
1954 Modified ONES:
https://en.numista.com/201597(This info is not posted on C&C nor on Numista. It is only found in the Charlton catalogue. Hope you can get a copy from the library!)
I read somewhere (possibly the CPMF) that the RCMP discovered this & ordered them to put the
FPN back on the plates! This is why only a small range of serial numbers within the 4 prefixes listed by Charlton have missing
FPN.
I purchased 3 fairly common
*B/M replacements, which I later learned had
no FPN (making them a tough variety)!

I posted the 3 notes in that link I provided to my collection & you can check it out here:
https://goccf.com/t/450797&whichpage=3#39036221954 Modified ONES with
no FPNCBN W/N prefix*
BABNT/M prefix*
U/M prefix*
*B/M (forgot the # range but I believe the # range is 0400000 to 0420000)
* I do not recall the # ranges for the notes that have been discovered on the non-replacement
No FPN notes but I do believe that they're quite scarce since their Book Values are quite high. The
No FPN notes for the regular W/N, T/M & U/M full run prefixes are far tougher to source b/c so few collectors kept those. Added to this: the
No FPN info only came to light about 10 years ago, so there are many coin shops, coin collectors & others (who don't pick up/read their Charlton or don't go to the banknote forums) who have no idea that they may own a tough
No FPN prefix!
I think that's kind a cool (esp if you like to shop on
ebay for tough notes)! I have seen a few collectors (who do know about the
No FPN prefixes post ones they found/bought on
ebay (for a pittance) b/c they have always been looking for a bargain.