Similar experience here: Does it Violate Any UA Rules (MP or CoC) if I Break a MP Ticket into 2 Separate PNRs?

I never knew that Combinability meant reading the fare rules. Now I do. Thanks!

It is a struggle for those of us in non-gateway cities. Years ago, it seemed that really did not matter too much and sometimes even better fares exist. Now, it seems a through-fare costs more than buying 2 fares (ideally on one ticket). I also remember when UA first started doing PE, PE fares between TPE and SFO were significantly lower than if you had an additional domestic leg in Y. I am not sure what it is now.