I know maximum man might not like it
The Sentry is Odin and Surtur combined into one being from their big fight. Odin is containing Surtur. It explains his duality. It explains his power level. It explains why he looked like Thor in his prison cell. And it explains why there's that giant sword behind sentry when he is holding a skull on one of those new covers.
I'd really like that. I don't think that's the case, but I like it.
So in this theory would all memories of the Sentry from before Odin's death by fabricated? Even disregarding those memories, the Sentry's first real appearance in MU-616 was before Odin's death.