Sorry, I'm a little slow sometimes. Okay, so I've pulled up the e-ticket receipts on BA's web site (of course it asked for the credit card number so I had to track that down!). It doesn't say "form of identity" on it anywhere, but it does show "card number" with the last four digits.
I tried to pull it up on the CX site. I can find the reservation, but then it asks for the e-ticket number to get specifics. It defaults to a prefix of "160" or "043"; but my e-tickets start with "125" so it won't accept the number. Now what?