I have noticed this as well but i think its because the serial number data-base is fairly new, it was not used back when BEP notes were hitting circulation. Actually there were a fair amount of BEP's around and therefore there was no need to create a register in WIKI site for this prefix unlike the BEL and BER prefix which appeared much rarer. Actually today in wiki there are 79 BEL notes reported, in the serial number db only 49, so yes the serial number db should be updated.