That agrees with what I found as well. The problem is that within the US model, phones sold through Verizon had a non-unlockable bootloader, (unless the workaround mentioned above does work), and there is nothing different about the model number, and not even a Verizon logo on the back or anything that will tell you whether the phone came from Verizon. This is different than, say, Samsung model numbers where they are specific to various carriers.
I did buy the phone I mentioned above, and although the OEM unlock option was greyed-out at first, after I tested the phone with stock ROM and a sim card, it was no longer greyed-out. I got /e/ installed on it with only one minor glitch – the most recent build of TWRP, twrp-3.3.1-0-sailfish.img, caused errors and failed to wipe the phone. Following advice from elsewhere, I used build 220.127.116.11 instead. This still indicated a couple errors trying to mount something - /volume maybe? But in the end it said “successful” and everything appears to be working.