So the official explanation is that they've spread all their purchases over a longer term. So if someone cost £100 million and the contract is for 8 years, the way the deal is structured, they're only paying £1.25m a year. So within the rules and according to the FA, they didn't spend anything more than £1.25m that year. And because they structured so many deals like that. They're more than okay FFP.
Obviously the FA didn't like that so capped it at five years, so that's what they've done with the newer signings.
It's important to remember rich people never spend their own money and will leverage their assets. They're basically mortgaging their players.