Phones of major vendors sold in EU still contain carrier info for the region even if they're sold unlocked. Outside of US and China, Samsung for example ships

Phones of major vendors sold in EU still contain carrier info for the region even if they're sold unlocked. Outside of US and China, Samsung for example ships so-called "Multi-CSC" variants of their devices which permanently apply the region and country of your device on first power-on with a SIM-card. The required information for that is not pulled from the network but is already preloaded in the ROM of the device, a network connection can be used to get an updated version of these profiles though