Thing is, people are always suggesting things like that, and it never turns out to be true.
"How can Strax be back, wasn't he killed in Good Man?"
"It's obviously Strax from before Good Man."
No, it wasn't.
"How can Osgood be back? Missy killed her."
"It's obviously Osgood from before Death in Heaven."
No, it wasn't.
This even goes on outside Doctor Who fandom:
"How can Agent Coulson be the lead of Agents of SHIELD? He was killed in The Avengers."
"Agents of SHIELD obviously takes place before The Avengers."
No, it doesn't.
Why do people continue to cling to this theory when they are proven wrong every time?