In most of the flashbacks, there was at least one clip that was not from a previous episode.
Goof: Amongst the videos Irving compiles of Phineas is him talking about the car of the future. This shouldn't exist as it happened in the dream episode Phineas and Ferb Get Busted.
It could be correct to say that Phineas is now eleven years old, as the episode Phineas and Ferb's Quantum Boogaloo reveals that he and Ferb are ten years old during the present time, and likely took place during the previous year.
Candace's busting attempt ended in a way similar to that of the episode "Traffic Cam Caper" in that her concern for Phineas takes over her desire to get him and Ferb in trouble.