@bbcsport_david
Lampard "signed" for New York City FC in July but with the new MLS season not starting until March, he joined Manchester City - who part-own New York City - until January.
Crucially, this was not a loan deal but a short-term contract signed as a free agent. It is understood the contract was for the entire season, with a break clause that was agreed would be activated at midnight tonight.
City needed that break clause removed if Lampard was to remain with them, which happened today.
But there was no need to re-sign him or re-register him with the Premier League because he was already on a contract until the end of the season and therefore registered as a City player - eligible for Sunderland and beyond. All that needed to happen was removal of the break clause.
Amendments to existing contracts require Premier League board ratification, which happened today.
All of this calls into question the exact nature of Lampard's signing/contract/agreement with New York City.