I have come to understand that linking PNRs is kind of meaningless. Found the information using a Google search pointing to this forum rather than the forum search function.
The reason behind my asking is seat assignments and the Chase Mileage Plus Explorer cc benefit of one free bag plus one for a companion. Looking at the United site there is no way to check the second bag for free. We continue from LAX to KOA on Delta which will allow two checked bags on a revenue ticket with the AMEX gold cc.