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Awesome! That was 99.9% of it, yes.

The only nuance that I'd add is that with OPC, the PMKSA is pulled from the AP to which the STA associated originally and pushed to other APs (as determined by the WLAN controller). A new PMKID is given to the same PMK based on the new AP's MAC (BSSID) address, and then the 4-Way Handshake ensues after the new AP receives an association request with the new (and correct) PMKID is included with the RSN IE.

In a nutshell, PMK Caching is "fast roam-back" as Brett C. has described. Opportunistic PMK Caching is "fast-forward roaming". ;0)

Devinator