This couple has been on my mind for many, many years now. I've been reading this thread for quite a long time now, and I finally found the courage to share my thoughts/ideas on who they were and what happened to them.
1. I don't think they were ever reported missing, meaning we will not find them in any missing persons database.
2. I don't think they are any of the missing couples mentioned here before. To me, they don't look like the McMinns or the Yakimchuks. I think they do look like the missing couple from Argentina. In my eyes, Jane Doe and Maria Marta look pretty much like twin sisters, but if you take a look at this video and skip to 01:28 or 02:14, you can see that Maria Marta doesn't have any moles on her face. Jane Doe has two distinctive moles on her face and that's why I think the Argentinian couple can be ruled out. Video is called Desaparición Forzada | Marta Vasquez - Trailer and you can find it on Vimeo. I can't post the link for some reason.
3. I don't think they were American, but I do think English was their first language. If it wasn't, someone would definitely be able to point out their foreign pronunciation. I started learning English 20 years ago and my accent is still rather obvious. People ask me where I'm from all the time and I think they would ask the Does as well.
4. The couple shares some similar features and that tells me they come from the same ethnic background. They look Middle Eastern to me, perhaps they were originally from Israel or Iran? If you look up 1970s Iranian fashion, it looks a lot like Jane Doe's style.
5. Like I said before, I think their mother language was English and I think they could be Middle Eastern. Maybe their families moved to a country like Canada and lived near the Middle Eastern minority? Maybe someone still remembers them?
6. Initially I thought it was weird that the KOA campgrounds employee claimed to be friends with Jock, but didn't know anything about Jane, not even her name. Where was she the whole time? Then I realised that if they really were from the Middle East, then perhaps it wasn't okay for them to talk to people from the opposite sex. It's just my thought - I'm not an expert when it comes to foreign cultures, but it would explain why Jane wasn't there when Jock was talking to the KOA guy.
7. Why weren't they wearing any underwear? Did the killer(s) take the couple's underwear as a memento?
8. Their gunshot wounds look... precise. It makes me think they were executed in cold blood. It also makes me think if they were kidnapped and tied up before being killed. Or maybe there was more than one killer and the couple was shot in their sleep. I suppose their wounds would be much more random if the killer just approached them and started shooting. I'd think at least one of them would start running away and their wounds would look different.
sorry for any mistakes in grammar or spelling, English isn't my first language so please bear with me ^_^