Serial number help

[2ac]

Glad to see the site updated and now I’m officially a member
I picked up a 90’ Yo frameset and seem to have a few people stumped on the serial number. Apparently the 90’ numbers were lower when a “Z” where used...?

 

[THO]

For what stands the Z????

Frame type : Yo Eddy Team
Frame number: 034Z07
Year of manufacture: 1990
Frame size: M (17")

 

[I-ROBOT]

I'm not sure on this one. I didn't have anything to do with numbering. Somebody on this site has the old serial number records
That frame does have the old pressed in bottom bracket so it is an early YO

 

[2ac]

I have seen the records and Z stops at a lower number