Yes. I don't think any American service provider does the carrier/SIM lock anymore unless they sell the phone to a new customer
And I'm sorry, I didn't actually read the whole thread and just read the OP. I feel like it's very awkward to do this, but I did find some way to check IMEI against a database. I don't know if this method is actually reliable and safe or not. I just tried it with my old locked Pixel 5 and it worked. Hopefully this helps you.
Plug [IMEI] in here: https://www.imei.info/
Click on Google Pixel SN & Warranty
You should see the network under the network description.
The record for my old phone:
See, next to "sales model" it says US VZ, so it's a Verizon locked phone.