The moment Marty went back into time and met Doc brown, it changed Doc Browns timeline, so he definitely ed everything but simply played along until Marty came back with the time machine.

Now, in my opinion, the Back to The Future series has plot armor more so than plot holes. For instance, we all know that the timeline of Marty's parents was also changed, and he became a successful book writer, etc. So you mean to tell me that George Mcfly and his wife still purchased the same exact house in the future after the timeline changed? Its possible but IMO Not likely since George was a completely different version of himself. It would have been interesting if his house would have been in a different location and Marty would have to look in the yellow pages to find it. Also in part 2, with Biff stealing the time machine and bringing it back to the exact same spot, leaving the car and his cane in the car, so that Marty and Doc can conveniently find it and notice that he stole it? No way Biff could have been that dense, but then again, it is Biff we are talking about, right? 😂😂