Finally I have a couple of BEST cores and am suddenly attuned to all things IC related. So much variability, so many keyways, and so much skill to be acquired to conquer the almost limitless picking challenges. I feel really late to the party on all that BEST has to offer.
Anyway, I realized that I have had a Yale core all along in my pile of miscellaneous locks. It has two identical keys with bitting for six pins. Neither touch the seventh pin responsible for moving the retaining tab. That pin can be lifted with a pick when turning the key. The back of the plug has a little triangular notch cut out of it. If a control key were used part of the retaining tab would slide into that notch to prevent further turning of the plug just like the BEST.
What other IC systems are out there?
Here are some pictures for your enjoyment.