Faz No5 serial number query

I have recently purchased an 8/46 dated No5 MkI ROF (F) with an X prefix and a three digit serial number. All the information I have read refers to a prefix and four numbers does that mean that my serial number should have started with a 0 or does it mean that the serial number range will just run to a maximum of four numbers?

Up to 4 digits so 1 to 4 numbers, no zeros in front, first 1000 had a FE prefix (preproduction) then started with no prefix then though the alphabet (A though Z but a couple of letters not used) then AA, AB & AC might even be some AD prefixed as well.