Hello. Is it possible that when booking a round trip A-B-A, you see fare class L=9 in all segments, outbound and inbound, but eventually priced as fare code=S, even all flights are UA metal?

If so, where can I find the exact fare code/fare rules for this L? I tried farecompare.com/search/flyertalk, which doesn't know the existence of L. Could it be possible that L is "unavailable" and .bomb is just demonstrating its "bomb" behavior?

Thanks!