There's no denying that Moon Knight is one of the wildest characters in the Marvel Universe, but fans might be surprised to learn that his dissociative identity disorder actually makes him retcon-proof.
Moon Knight's origin story has evolved and shifted over time, but the basic premise behind it has largely remained the same. Mercenary Marc Spector is betrayed while on a mission in the Egyptian desert. Desperate to save his own life, he makes a bargain with an ancient Egyptian God named Konshu to become his avatar and punish wrongdoers. Unfortunately (or perhaps because of Konshu's intervention), Marc's dissociative identity disorder makes his vigilante activities difficult. Given that Khonshu is even more mythologically inaccurate than Thor, there are even some questions of whether Khonshu really exists at all.
There have been many different writers that have taken on Moon Knight over the years. These interpretations have been wildly different ranging from an analog to DC's Batman to one time where Moon Knight became his own Avengers team. Moon Knight has also been known to take on new personas such as the street brawling Mr. Knight. Fans might view all of these different sides of him as contradictory, but in fact everything could be explained away by Marc's mental illness. For any other character these changes could be considered retcons, but they align perfectly with Moon Knight's propensity for change.
Even abrupt shifts in Moon Knight's origin can be tied back to his illness. While most characters that have a change in origin might see some wild explanation to justify the alterations, many of which are quite obscure and beyond belief, any changes to Moon Knight's origin could be explained through another personality. With all the different identities swirling inside his head, Marc Spector's memories could easily be altered. So any "retcon" could simply be attributed to that.
Interestingly, other characters in the Marvel Universe also have this ability. Most notably, Kang the Conqueror is seemingly immune to retcons as well. This is because of Kang's time-traveling abilities. If a new writer comes along and changes anything in Kang's past it could be written off as him doing it himself through time travel rather than a retcon. But where Kang and Moon Knight differ is that Kang's retcon immunity is through something he does. With Moon Knight, he is immune to retcons just because of who he is as a character.