Without getting into the last half of your post, a check that is payable to A/B is treated in most states as an item that fits this definitional sentence in Section 3-110 of the UCC: "If an instrument payable to two or more persons is ambiguous as to whether it is payable to the persons alternatively, the instrument is payable to the persons alternatively."
The virgule (slash) is ambiguous. It means neither "and" nor "or." So it should, in most statements, be treated as if "or" appears.
Bank counsel should be able to determine what the case law in your state has decided.
_________________________
John S. Burnett
BankersOnline.com
Fighting for Compliance since 1976
Bankers' Threads User #8