Just noticed this when trying to book a last minute ticket. MIA-ORD, B fare costs 900+ while L costs 1000+. EF further confirms this:

AA1044 F1 A0 P0 Y2 L2 B1 H0 K0 M0 W0 V0 G0 S0 N0 Q0 O0

From other sources, B should be considered as full fare while L is only 6th tier. Has that changed?

Thanks!