I saw an engineer from WWV speak to the local radio club a few months back. If they did for WWVB what they did for WWV, a big stack of QSL cards was printed at one time. It's why WWV had the same card for decades, which he reported they finally ran out of, but it sounded like he wasn't thrilled with whatever new design they came up with. He wasn't thrilled with the old one either, so take that for what it's worth.
Anyway, I should QSL them sometime.