This might be nothing or it might be something, I don’t know. I’ll put it out there anyway, just in case it turns out to lead somewhere.


One marque that used this kind of serial number format was PT (Percy Thornley) Stallard.


I always thought Stallard stopped making frames sometime in the mid 60s but it turns out there were Stallard frames being sold into the late 70s, with some rebadged (maybe even imported) ones being sold under the Stallard name in the 80s.


In any case, Stallards with a “Z” prefix were the Zakopane model. The first two digits following the letter were reversed and indicated the year (early ones had only one year digit) and the remaining 3 were sequential numbers for the frames made in that year.
So, as speculated earlier in the thread, Z07022 would indicate a 22nd Zakopane frame made in 1970. Here's a number from a 1964 Zakopane (also, incidentally, in Australia and also with Campagnolo droputs):





Now, there are very few examples of Stallard frames online from what I guess you’d call the “late period.” Generally few frames had the wraparound stay treatment (I've seen one from 1978 and one from 1967) and a few a little older than 1970 that use the same fork crown, as you can see below (also, the squared off cable stop on the chainstay was common on British bikes and can be found on most Stallards):

1978 Malvern:



1967 Cotswold:



1966 Cotswold:





Unknown:




Finally, that shifter band clamp stop certainly is unique; I've never seen one like that before. Perhaps it's my eyes playing a trick on me (or it's just a bit of wishful thinking on my part), but the stop on this 1978 Malvern seems to protrude a bit...




Also, Percy’s brother Denis lived in Perth and was the distributor in Australia, so there’s a better chance of finding a Stallard in Australia than maybe in the US.


One cool thing about the Stallards is that all the build slips still exist and you can have a frame number verified (apparently there’s a small fee) by contacting the Wolverhampton City Archives.


Again, maybe I’m way off on this (as I have few reference points), but who knows.