Since the T,W,Th vibs are now included in the VBK that ran on Fri, is Thu the only version of that file now available?
Friday synthetic full includes only Friday version of the VM. As synthetic full does not trigger deletion of the older backup chain, after synthetic full on Friday you will have all version from N last backup sessions (N is your retention settings). For example: if your retention is 5 backups, then by Friday you'll have version from Monday, Tuesday, Wednesday, Thursday, and Friday. Pleas check this animation
and this article
for more details on how retention policy for forward-incremental works.