On Tuesday, the Dallas Cowboys, and every other team in the NFL, set their initial 53-man roster, but the reality of this situation is that things are going to change a bit before they finally settle into place.
As an example, the Cowboys are likely going to place certain players (Matt Waletzko and Nahshon Wright among them) on injured reserve, but they had to be on the initial roster to be able to return from IR at some point during the season. This is why the Cowboys initially cut players like Chuma Edoga, Trent Sieg and C.