I'm booking a flight (US domestic), and I want flexibility to confirm a same-day change. When I use the advanced search to restrict to higher fare classes, I see a flight with the following results:

Economy--L class, $144 (fare basis code LAX2PKEN)
Requested fare class--B class, $224 (fare basis code LAX2PKIN)

Should I be worried that the fare basis code for the B class fare starts with an L? Is there a good guide for interpreting United fare basis codes? (The guides I've read on blogs all say "the first letter is your fare class," so either this is an L class fare or I'm reading bad guides.)

I just want to be sure my fare will read as a B class fare in the UA system, since that's far more likely to be available for same-day change than an L fare. Thanks!