Right.  Until about 1989 or so, US occupied just a handful of gates in B.  Was there even a hammerhead at the end at that time?  I recall TWA might have even had a gate or two in B.  Continental was in C with some others.  There was no A (until 1991).  I think Eastern and PA might have been in B or C, too.
It was around 1990 that I think B and C started becoming taken over by US.  I don't know when exactly CO and TW moved over to D.  I think MAC was also in B at one point.  Some astute US historians will know better and clarify this for me.That didn't change the economics, though, and it won't for CLT when those days come.