When did Marvel's Satan get replaced?

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So in 1968, Stan Lee himself introduced Mephisto. Pic related exposits his implied position in the cosmos. He appeared in the pages of Silver Surfer and Thor.
Then in 1972, Roy Thomas replaced Stan as Marvel's EiC and Ghost Rider was introduced as a man who sold his soul to Satan to save his adoptive father from cancer. At some point, "Satan" was retconned to be the pre-existing Hell-lord Mephisto.
... but in issue #2 of Ghost Rider's self-titled series, it's revealed that Satan has a son, Daimon Hellstrom. Helly's father has never, to my knowledge, been Mephisto. So when was the Satan from Ghost Rider changed to not be the original leader of the fallen angels, and how many retcons has Hellstrom been through?