UA MP was showing only one ticket for adult + lap child. Bought that for wifey, that cleared in I. Bought a Econ B fare, tried the SAUA and low and behold to my surprise that cleared despite no more UA inventory. I know it's a bit risky if there's IRROPs, but will call them to make a note to tie our reservations/seats together. Crazy whimsical - don't get it, but got the RL, so all good.