how do i know if my phone is unlocked BEFORE switching carrier

I am joining a plan of my partner's. I paid off the device officially today. I know that "supposedly" my phone will be unlocked in 48 hours, and that the best way to test if it's unlocked is to try a new carrier SIM card. However, I have read horror stories where the person transferred their service after the 48 hours when they tried the new SIM, it turned out the phone wasn't unlocked, but since the service was already transferred, Xfinity could no longer unlock it. Can Xfinity not confirm BEFORE I transfer the number to get the new SIM that the phone is indeed unlocked? It is an iPhone 14 Pro Max. Thank you!