One of my classes had a midterm scheduled right after we were all sent home due to Covid-19. The professor said that for this midterm, we were allowed to use notes, both his and our own, browse the internet, and talk with peers during the exam. While this seems abnormal, we, as a class, checked multiple times and he confirmed this policy every time. Thus, during the exam, about 2/3 of the class (~10 people) got in one video call and were talking during the exam.
For the final, the professor simply said that the rules would be the same as the midterm listed above. To our discredit, no one double checked what the professor meant and simply went with it. Of course, the same ~10 people got on the video call again and did the final. It was not an easy final, despite us collaborating and looking at notes, leading me to suspect nothing wrong. The professor also had not posted a note saying collaboration was allowed on the exam, although this was the same as the previous midterm, so I thought he had just overlooked this. Looking back, I see the fallacy in this, but it did not seem important at the time.
However, recently I was talking to an acquaintance from the class, one of the 10 in the video call, and I found out that he had indeed checked with the professor about peer collaboration on the final, which the professor explicitly disallowed (this was during office hours). This acquaintance said he did not tell this to us as he needed us helping him on the final to pass the class.
I'm conflicted on what to do now, as it has been over 3 weeks since the end of semester (4 weeks since the final in question) and most of the class was in on the video call. If anything, all our answers were EXTREMELY similar (most were exact copies) to the point that it would be obvious we were collaborating. On one hand given the above, it seems unnecessary to dig this up. On the other hand, I'm not sure that I'm not reasoning my way through having cheated. Please advise.