Upgrade Cost Differences on Same Plan

I am still on the 5G Play More Plan with the Disney Bundle on an account with 4 devices. All of us have iPhone 12 Pro Max's we got at the same time with Verizon when those came out, and I was able to get the $999 off a new device towards the 16 Pro Max on launch day. The other three people want to upgrade now too, and two of them on my plan are able to get the same trade in deal I did, but for some reason one of the phones is only getting a $1000 deal if they switch to the new Unlimited Plus plan. Any idea why this one phone isn't getting the same trade in deal as the rest of us?