Well I think it will grandfather the old owner. If you check the mbn github repo, there is good list of SD835 carriers to flash. I believe OP5 was supported by Norwegian and Swedish Telenor.Not
Not sure for other SD835 devices, will have to ask people on different forums as don't think i could find out from first hand, and about brand don't know much about transactions and if they using someone else's equipment, i only know that earlier for more years was good brand Telenor from Norway, but someone bought their part on Balkan 2018, which renamed into Yettel just now month ago, even if they still had just brand name Telenor till now, it wasn't that good like earlier, so i'll have to investigate that, thx for tip
But its important to have twrp present to backup the efs if something happens.