Can anyone explain the criteria AA uses to determine if a cancellation becomes a Flight Credit or a Trip Credit ????

Originally, I had two Flight credits:
#1. DCA - KOA (purchased pre-covid; extended out to March 2022 with the blanket extension AA provided last year)
#2. PLS - DCA (a return ticket purchased and cancelled in May 2021, because I took a United non-stop)

When AA announced "Trip Credits" last month, #2 above became a "Trip Credit", with an additional 3 months added to the expiration date. #1 Stayed a Flight Credit. OK, no problem, Trip Credits are actually better. I assumed #1 stayed a Flight Credit because it was purchased pre-covid and was in the blanket extension AA gave last year.

This month I purchased and cancelled Trip #3:
#3. DCA-PLS, Aug 2021.

Inexplicitly, AA credited #3 as a Flight Credit. I had guessed it would be credited as a Trip Credit, as I thought that's what AA was going to. (??) Part of the reason I purchased this while knowing there was a high probability the date or destination would shift, was thinking it would be easily combined as a credit for other stuff coming up.

Fortunately it's not really a huge deal with the trips I'm hoping to make this year. Still, not as convenient and simple as a Trip Credit. But going forward, ideally I'd like to know what my refund mechanism will be, even before I purchase a ticket, but definitely before/during the cancellation process. Now that there are "choices".

The only obvious distinction from my three tickets is the one Flight that didn't originate in the US was refunded as a Trip Credit. But it seems a stretch to assume that is a criteria.