A family member purchased a few B-class fare on United for the upgrade without co-pay purposes plus it was just marginally more expensive than the L-class offered (surprisingly). I was looking at their ticket online and the fare rules basis code and it says SLX00 something. The fare class on the itinerary still says: United Economy (B) and allowed them to upgrade without copay.

Is the Fare Class (B) used for accrual purposes or the underlying Fare rules first letter (S)? I know for accrual to United is based on ticket price but they are accruing to another star carrier.

thanks in advance for any experiences with the above scenario.