Yep, it's clearly showing GTM 2.20, but irrefutably the 006B154600.GCD file from your returned unit which you've uploaded in Post #33 is identical to Garmin's V2.30 GCD file which is named "FirmwareUpdateforGTMxxDigitalRadioTypeS_230" in Post #1 and you can easily compare them yourself in both hash and hex to confirm that. My guess is that 2.20 naming was used by Garmin as a recovery 'downgrade' firmware, but it's still really 2.30 because that's proven by the hash and hex compares. I also reckon that yours and gette's receivers weren't the only GTM70s bricked by loading the GTM60 firmware courtesy of GarminExpress so you may not have received your original receiver back, possibly it's a 'refurb unit' which would explain the relatively fast turnaround.

Garmin has a history of remaining tight-lipped on this sort of stuff up. They generally quietly fix or exchange any problem units resulting, thus minimising 'bad press' collateral damage. I grudgingly admire that corporate philosophy quite frankly ......

PS: I removed your Unit ID from your image, not good to display that publically.