I think that's how Beckett numbered them in the magazine. From memory, there were only 27 teams at the time, if you a winner from a contest card, you received a set like the Jordan you have, but with 30 cards. The Exchange (XCH) had more cards than the contest set, but every version was grouped together in the magazine and XCH was to inform that those three didn't exist as contest cards. Those three letters aren't on the cards. Whoever copied the checklist from Beckett to TCDB didn't do their research, so these checklists are off. Someone else can correct me if I'm wrong, but this is how I remember it.
I'm going to reevaluate how I collect after the new year. It's just getting way too expensive for the new stuff. Sometimes I just want to buy a pack, not a whole box or even blaster.