I thought FIFA had a rule that transfers were only allowed during 2 windows, summer and January. Or was that a UEFA thing? Or do MLS trades not = transfers? Or are we completely below the FIFA radar?
Two uneducated guesses until someone more knowledgeable answers: 1) Since all players are contracted to the league, it can be argued there was no transfer as such. 2) It's our off-season so the rule may not apply within MLS right now.
It's a UEFA thing. Each league is allowed to set its own two transfer windows. The major transfer window is the league's offseason. Leagues are allowed a second transfer window during the season.