Well color me shocked. I successfully PC from the CSP to Chase Freedom Flex last Friday. And then I re-read the 48-month restriction (time from BONUS RECEIVED). Dug up my old statements but they didn't have the exact date. Seems I had opened the "old" card in April of 2019. I had the May statement (technically ending June 2nd) that showed me getting the bonus 50k points. Payment was received on 5/26 of 2019. So I was kinda sweating applying.

Yesterday I applied and was approved, so I guess I'm good. Only thing I can think of is that the bonus 4 years ago was $3,000 spend for 50k points and I must've met it (the April statement was like $2700) around beginning of May.