And that could work both for and against Pompey in the coming weeks, as they undertake their summer business.
Danny Cowley has indicated he’s keen for the Blues to get their recruitment work done early as his faces another busy summer strengthening his squad.
But the league this year will fall into line with international transfer regulations - and that means no new signing can be confirmed until the window opens on June 10.
That leaves players open to agreeing deals in principal with clubs, but then using that agreement to drive up their earning power elsewhere.
Cullen explained Pompey will do their best to keep deals close to their chests, but there will be a degree of uncertainty until those moves are officially over the line in four-and-a-half weeks.
He said: ‘The big change of dynamic in terms of the way football operates in the EFL is the transfer window has become more rigid.
‘In the past you could sign a player from another club or a player who was out of contract, as soon as the season finished in the EFL.
‘But Fifa last year put pressure on the FA to tell the EFL to come in line with international transfer regulations.
‘So now the date is June 10 (when the window opens).
‘So you can do your business with your own players, obviously.
‘With anyone new you want to register, you can have those discussions with the players if you’re looking at a transfer fee being paid and you can have those discussions with clubs.
‘But nothing can be signed, sealed and delivered until June 10.
‘So you can have a deal technically agreed and the paperwork signed before, but it doesn’t mean anything until June 10.
‘So we’re conscious as much as we can that we keep our business fairly close to our chest, because all we could do is getting something there and have it agreed - but you could still be prone to being hijacked in that interim period.
‘That’s a bit frustrating because you’re keen to get the business done in May if you can.’
Cullen acknowledged that while Pompey will be hoping they don’t see deals scuppered in the coming weeks, the new regime could also potentially work in their favour.
He added: ‘You do have the other situation of players who have offers who will use that period to explore other options.
‘They may feel the grass could be greener somewhere else.
‘Hopefully we get a few things done, but there will be a natural desire from some players to say: “well, I know what that club’s offering - what can Portsmouth do for me?”.
‘It’s a real weird one, but it will not stop us trying to get into a good place and get things done.’