After Lampard's release from Chelsea, NYCFC announced in July that he had "signed a two-year contract which starts August 1st" and paraded him around Manhattan.
In fact, he'd only agreed to a "commitment" to play for NYCFC on a two-year contract from January 2015, the player and City Football Group said on Friday.
The uncertainty over the midfielder's status emerged only after his surprise switch to partner club Manchester City, which was initially wrongly described in August as a "loan" from New York, was said on Dec. 31 to have been extended until the end of the European season.
But English Premier League rules state that Lampard's contract had to run until June 30. After the Premier League looked into the issue again on Friday, it was further clarified that Lampard's deal had always been for the whole season, but with a Dec. 31 break clause that could have enabled him to return to NYCFC for the MLS season.
Both teams are part of City Football Group (CFG), the umbrella company for the portfolio of clubs owned by Abu Dhabi's Sheikh Mansour.
CFG acknowledges that Lampard's only playing contract is with the Premier League champion, with the midfielder's MLS career not now due to start until midway through the season in July.
CFG told The Associated Press that the NYCFC announcement last July "was a genuine error which throws everything into confusion (for media and fans). It wasn't a contract. It's an agreement with City Football Group with intention to play for NYCFC."
Lampard's move to Manchester City was remarkable because only days earlier last summer he said the MLS move was because he did not want to play for another Premier League team after 13 years at Chelsea.
"When released from Chelsea last year at the end of my contract I signed a commitment to play in NYCFC for two years starting January 1st 2015," the former England international said in Friday's statement.
"I was then offered the chance to train and be part of the Man City squad in the interim to keep myself in the best shape going into New York. This period has since been extended by Man City and I now will start playing for NYCFC at the end of this current Premier League season."
Despite City Football Group acknowledging its mistake after a week of silence on the issue following inquiries from the AP, Lampard said he had read "a lot of lies and nonsense over the last few days."
"There has always been a constant dialogue between all parties in this time to find the best solution for everyone," Lampard said. "I can say that I am very excited about arriving in New York."
NYCFC supporters' group, The Third Rail, said it was "outraged" by Lampard's prolonged stay in England because July's misleading signing announcement was accompanied by a push to sell season tickets and the player's jerseys.
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