If we have a rate lock that is extended and is at the same rate, is the date we use for the APOR and rate spread calculation the original rate lock date or the date the rate lock is extended?

The small entity guide says "date the financial institution exercised its discretion in setting the rate for the final time before loan closing or account opening" but I still am not sure which date that means!

You reset the rate when the lock was extended. Whether the rate changed or not, that is when it was set.

Agree!