Uhm actually, Magneto's continuity is a bit more complicated than that.

When the comic first gave his background, he was said to be jewish, and a concentration camp survivor. This includes flashbacks to after the war, where Magneto is living in Israel for a while; this lasted for several years, until some writer thought Jewish readers might mind him being a bad guy, so they backtracked to him being Romani. Then when Jewish readers were upset that Magneto was taken away from them, he was returned to being Jewish. But it was said that his wife Magda, aka Pietro and Wanda's mother, was Romani.

Then during the Joseph years, we found out that Magnus was never his real name, but just one he used to hide his original name.

Now the name Max, comes from a damn good Magneto miniseries called Testament, where the writer fills out his childhood, and his life up until after he escaped the camps. It's a harrowing tale, about the death of his family, meeting Magda and surviving Auschwitz.

It's also one of the main reasons that lately they hesitate in turning him back into a full villain.