For $29/mo, we provide access to advanced level technicians who will answer your questions on any Macbook board related matter to the best of their knowledge promptly & walk you through how to solve your problem so you can deliver a working board to your customer.
AFAIK when you buy a BIOS chip from eBay the SN is blank. Buy one, dump the file and flash that back to your donor chips.... Unless you know how to prep a BIOS for BBS.
When you sell or use the boards can't you just use the SN of the board it's replacing?
Why do they have to be unique now? Apple doesn't give a shit about these boards, as they are all vintage. Just use the same serial on each board, if it matches the spec. I doubt customers are going to cross check.
Because of issues with AppStore, Skype, Find My Mac, Messages/iMessage, etc. Unique serial number is important. It may not be "as" important on older boards, but certainly would prefer to not put the same serial number on multiple boards. Also for our own records.