I've not heard of JDJ rounds stretching frames, but of course they could do so if loaded too hot. I've fired about 1000 rounds of .300 Savage in one of my frames, all at max loads according to the manuals, and some factory ammo too, and the frame is as tight as when new. That's a nominal 46,000 cup with an '06 head size.
I did stretch a frame twenty+ years ago with hot .35 Remington and .45-70 "JDJ" loads. It was one of the weaker "old style" hard-to-open frames, and T/C replaced it with a modern easy open frame for free. So I do know what a stretched frame is. None of my current frames are stretched at all after many thousands of shots, but I don't do stupid things like overloading any more. If the fired cartridge extracts even slightly sticky, it is probably too hot.