How does the VAULT keyway backward compatibility work?

VAULT keys are backward compatible to InstaKey or Standard keyway cores

VAULT tapered keyways are precision-engineered and BMHA certified to fit original keyway cores, but original keyway keys do not fit within VAULT Door Technology cores. The tapered gate in the core keyway blocks the original keyway from entering.  Whereas, the tapered keyway key can enter an original keyway core.

VAULT backward compatible keyways work with existing InstaKey restricted keyways (E-K) or Standard industry keyways (A-M).