There is a U tubber who does a lot of engine dyno's testing various mods and engines. ( including turbochargers)
His name is Richard Holdener
He actually has a session explaining exactly why you are wrong with back to back dyno runs.
I first ran into this helping a friend. I saw the low power/torque gain and knowing he was doing a lot of " non- regulated " racing thought replicating it would help him.
I couldn't consistently replicate it and wasted too much time. Watching his video explained why.