Toughest deer I ever ate was cut up blood warm, packaged, and immediately put in the freezer. Every cut was so tough you could not get a fork into the GRAVY! Tasted fine, just felt like you were gnawing on Goodyear's finest all-seasons. Ended up turning it all into burger. Had to brown the burger, then bake in a covered dish drowned in red wine at low temps for 3-4 hours to change it from being rubber buckshot. Made casseroles from that doe.
She was also a deer that had survived some injury that removed her hind leg from the hock down and she had absolutely zero fat on her.
I am not surprised rigor is good, rigor mortis is not permanent, but is a normal reaction of muscle after oxygen has been depleted. Once rigor has completed, muscle relaxes and becomes more tender. For those of you down south that have never had a chance to eat a well aged venison cut, you are really missing something!