So here's the question: All games were tournament games (hence strictly everything), so what should be done? The noble thing - tell the opponent and load the autosave, or the ignoble thing - insist that they violated the rules and beg for a tech win?

p.s. I'd even say that this question is for the AC

Questions of nobility are for each person to decide for themselves.
Based on my judging experience, players usually come to an agreement among themselves in such cases and resort to the judges' services extremely rarely. But formally - if the situation is strictly defined by the rules and cannot be interpreted ambiguously, then a rules violation is punished with a tech loss. If, for example, the guard is not visible at all, then the judge decides based on their own experience and common sense (but not in this case - "I see that the passage to the adjacent zone is guarded by a shifted pile of dead bodies", meaning the opponent could also see it).