I'm not sure how US's BP's look (haven't flown them in years), but as long as your MP# or something like LH's "UAMP *G" (again, not sure of the exact syntax) shows up, you *should* be fine.

If for some reason there's nothing denoting your UA # on the BP, check with a TA or GA at the airport, and they can add it.

Lastly, hang on to your BP's (or print to pdf) until the miles post.

Hope that helps!