Once the new league year begins each year, the roster maximum is 80 players, until the two cut down dates towards the end of camp (to 65 then 53).
In addition to the 80 player maximum, players allocated to NFL Europe receive roster exemptions that last until near the end of the camp (not sure of the exact date). Hence teams can have more than 80 players on their offseason roster.
Now what can happen is that teams are reported as agreeing to terms with players, but they dont actually sign the deal until a roster move is made at a later date to free up a spot. I'm also not 100% certain that our draftees count yet as they are not under contract. Some combination of these factors would probably allow for the 4 or 5 spots we're over (counting the 80 spots plus our NFL Europe contingent).