Kelloggs really switched things up with the 1973 baseball cards.
They ditched the 3D format. It seemed like an odd decision, as the 3D cards were unique. The 1973s were no different that any other baseball card. Apparently they saw the foolishness of that decision because in 1974 the 3D cards returned.
The 1973 set has a couple other unique features. It was available not only in the cereal boxes, but also by mail-in. A couple bucks and a couple box-tops could get you the entire set. The mail cards also came in 3-player panels.
Billy Williams is on the checklist and I've had his card for years. But the panel version is also listed on the PSA master list and I didn't have one...
... until now!
The panel is perforated to make separating the cards a simple task. Thankfully for me the original owner of the panel didn't bother and I can check another card off of the master list.