Hi,
I've been following this thread. I don't see that you mentioned trying the built in reset function if it was still available.
Also did you try the serial number on the bottom edge of the tablet, that's the correct one.
Yeah, I've reset it using the built in Reset my PC and the Windows Defender Fresh Start. The one at the bottom edge of my tablet matches what the Surface app says and it doesn't show up. I've also use the one at the bottom of the base.
I wish I could just get what the product SKU is, seems weird that mine would start with OEMSHP. If that's what all these apps and firmwares are keying off of it would explain why mine can't get updated.