AAA0000000 allows enough possibilities to uniquely identify a banknote from 1982 through somewhere around 2100, assuming we don't suddenly print a few billion notes.
00000000000 was fairly quickly reaching exhaustion, at least for the $20s. It would not have remained feasible for long.
Look at it this way... Since introducing the AAA system, the A-- prefixes are almost totally saturated, as are the E-- prefixes. Since its design, each printer was left with several overflow letters, namely B, C and presumably D for BABN, and F, G, H & J for CBN. CBN has been making use of F-- increasingly, but G-- and H-- have so far only been used for three series of $5 notes each. BABN has used a few series in B--, and just one in C--.
This all happened over a span of approximately 25 years. The two-letter prefixes of the 1954 series were completely exhausted within about 20 years, and the two-letter prefixes of the multicoloured series were nearly exhausted within 12 years, even considering that the 1979 $5s and $20s made an early exit from that program. If they would have reset the system instead of adding a letter, I predict that it would have been exhausted in less than 10 years, probably to around the time the Birds Series was introduced. If the Birds Series used two-letter prefixes, the system would have been exhausted with only the $2 and $5 notes, leaving no room for the other 5 denominations, especially the $20, which ate up ~10 series all on its own.
With the 11-digit serials, it is really a 4-digit prefix and a 7-digit serial. However, since the first digit represents the denomination, and the second represents the printer and/or test/replacement status, the options become limited to just a few groups of 100 prefixes. The 1979 $20s used 50--, 51--, 52-- and 56-- in less than 15 years. If continued, I expect they would have been completely exhausted by now, if not a few years ago. The $5 notes used up half of 30-- and used 31-- and 33-- for replacements and tests. This was done in 7 years. When the Birds notes came out, and especially once the $2 was retired, the $5 note was printed in hoards. I'll leave it to you to figure out how fast they would have run out.
The point here is that AAA0000000 is 50 to 100 years more capacity than 00000000000.
(And if the BoC continues reusing prefixes such as ALA-ALZ, then it could go on indefinitely). <gripe>The system was perfect until they screwed around with repeating prefixes!</gripe>
Logged
BWJM, F.O.N.A.
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