The author needs to watch the movie again. Marty going back to 1955 was an accident. He didn't have a reason. He also came back before his alternate self went back in time and watched himself see Doc get shot, run from the Libyans, and go back in time. As for the main question, the most reasonable assumption would be that the alternate Marty went back and had a slightly different experience, but with the same result, which would then close the loop.

While it is true that it was revealed that he was innocent of the crime that got him put in prison, during his escape, he assaulted several prison employees, which would land him back in prison in the real world. Whether that holds in the Cobra Kai universe, where people regularly assault each other with no repercussions is up for debate.

There were a lot of things that made no sense when you think about it too much, even going back to the early seasons, but the thing that actually stuck out to me with this set of episodes was the announcement of the Russian team being disqualified being just a quick meeting in the hotel lobby and not a televised press conference.

The Vulcans "not lying" thing had been dealt with before. On Voyager, Tuvok started out as a spy on the Maquis ship commanded by Chakotay, which obviously required him to lie about many things. When Chakotay later asked Tuvok about it, Tuvok explained that he didn't consider it lying because it was part of his duties. I imagine the Vulcans in Enterprise would justify it in the same way.

Nothing is ever permanent in comics. Even death. This looks suspiciously like Chekhov's gold kryptonite, sitting above the mantle of the first act. I would not be surprised at all if this ended up with him being exposed and losing his powers "permanently", only to find some way to eventually get them back.