X70 4K upgrade vanished
 

I own three X70s; one of them purchased used from Adorama, with the 4K upgrade. I used the camera in 4K mode two or three years ago, but normally all of them are used in HD mode.

Today I was looking at all three of them to figure out which one has the 4K license... and none of them have it. I don't know which one was the upgraded one (since I purchased it used, the Adorama invoice doesn't list the serial number).

Is there a way I can find out which one it is and restore the 4K upgrade?

Thank you,