I'm not in a position to question either your or Ryan's research of the particulars. I just like to toss in general info about parachutes and their use.
Cossey moving a ripcord handle to make it less accessible to a student is reasonable, but he would not put it out of comfortable reach to the user. If he thought that he had, he could always move it back before selling it. All a user would have to do is put it on and familiarize themself with it.
Hayden wouldn't necessarily need his two rigs to be a matched set. He likely had one that he preferred and that he himself always wore. His second one was likely for when he took a passenger up for a ride. 'Meeting regulations' means he's required to wear it during certain types of flight. 'Never intending to use it' means he would never intend to actually bail out, he would prefer to work out his problems in-cockpit. I know both Bruce and Blevins interviewed Hayden, and Bruce has pictures of him with the returned rig on. Did Hayden ever say anything of that nature, whether that older one was the one he liked to wear or not?
Is it established that Hayden was indeed an aerobatic enthusiast? R99 asked about his airplane, and it was identified as a WWII trainer. I'm not a hundred percent on this, but I think that an old military trainer restored for civilian use might likely be classified as experimental, and that in itself might require him to wear a rig, even if he's just cruising in it. It would certainly be capable of aerobatic maneuvers, but I think a lot of pilots just cruise them. Kind of like someone restoring an old classic muscle car.