FatDad,
If I understand correctly, you used the 20-minute test to establish Threshold Pace 1, and then used the 10K results to establish Threshold Pace 2.
The threshold estimate from a race is just that: an estimate. It will never be as accurate as a formal field test. It’s not necessarily common for the 10K estimate to be lower than the 20-minutes, but it’s certain common for the 10K estimate to be different than the 20-minute test. I think it’s a testament to our calculator that it was so close!
The estimate from an event is a stop-gap until you perform the 20-minute test, not a replacement. So yes, use the 20-minute when possible.
David