When the demon cuts Phoebe's hair, he only cuts a small amount. When it is shown later it is a much larger chunk of hair.
Phoebe says she had curses for 4 years. She actually visited the uni for 2 years (second half of 2nd season to first half of 4th season).
Original goof {Sheridan comes to the manor with a still frame from the footage to say the girls were the last ones to see the councilman before he "disappeared."...There's no way Sheridan could have known the sisters had gone to see the councilman. All the security footage proves is that they were in the building}. Yet, Sheridan could have been bluffing to get information out of the Halliwells.
When Piper and Imara-as-Phoebe go to the city councilman's office, Piper freezes the reception area and then they vanquish Daleek. After the vanquish, they don't go back to the reception desk before leaving. Even if they didn't know about the camera, this would be exposing magic, as they would be there one moment, and gone the next when everyone unfroze.