Default Possible wrong flash from at&t s4

I'm wondering if anyone has any thoughts as to how I should proceed. I purchased a close to mint s4 that didnt read the sim card. It was cheap and I needed a screen for my s4 that I cracked. I tinkered with it a bit before tearing it down and other than no sim error the phone seemed to work flawless. When I did the tear down I noticed the internal screen housing was i337 stamped. The circuit board for the charging port was as well. The mainboard was stamped i337/m919 but the sim slot was stamped gt-19505. the imei on the sticker doesnt match whats in the settings. The sticker says tmobile but a search of phone info online shows the imei in the settings is from a i337. Does anyone know if this may be a possible flash thats wrong and the board was actually at&t? I'm aware you can change the meid easily and that may be it as well but im hoping maybe there is some software I can push to read if this is the case. I did order a sim slot to put in this evening and see if the slot is just bad. My old screen is not cracked bad and works without any issue so I would like to get it resolved and just resale it for parts on ebay is my plan if I can get the phone straightened out.

tldr-will flashing at&t rom brick the tmobile since the hardware is basically identical? Is there any way to tell if the wrong rom has been flashed to the board?


Booting into dl mode shows m919 and that knox hasnt been tripped. write protection enabled and emmc burst mode is enabled so I'm going to assume its not been flashed.