Many articles indicate that teams like Philadelphia are over the salary cap. This leads to confusion as to what the rules allow. The truth is that Philadelphia is not and never has been over the salary cap. No team may exceed the salary cap at any time.
Philadelphia actually rolled over $514K from the 2017 league year into 2018. It complied with the salary cap in 2017, though just barely. By comparison Green Bay rolled over $3.934M. The reason the sports articles describe the Eagles as being over the salary cap limit is that the team will be over the cap as of March 14, 2018 if they do nothing.