I doubt people will read this, but if you really want to the game of chicken between club and player, and why VVD and Coutinho are nailed on to move next summer if they want to, read on.
Legally VVD could sue Southampton if they didn't sell him next summer after handing in a transfer request this year.
The whole transfer system is borderline illegal as it infringes on employment law - UEFA, FIFA and the clubs knows this, and operate accordingly. Player's unions are trying to get it reformed, and in the future there will be a more formal system regarding transfer requests.
What is a transfer? It's compensation for breach of contract. "We had this guy under contract, you want him, and in order for us to agree, we need to be compensated".
Players can't just up and leave for free mid contract because a) compensation and b) non-compete clauses (can't go to a rival company for a certain period of time - this is known as a restrictive covenant).
However, restrictive covenants are limited in time. This is the kind of thing which stops a big CEO going to a rival for 6 months, or a salesman jumping ship and poaching clients for several months. Some of you might have non-compete clauses in your work contracts. Same thing applies to footballers. However, they're only enforceable within reason - 6 months, a year maximum - and not for 5 years or the length of a footballer's contract.
So Van Dijk wants to go now. He could quit (yep, footballers can quit if they want to, just like any employee) - he'd forego wages, Southampton would sue for compensation (they did pay a transfer fee after all) and UEFA / FIFA wouldn't let him register for another team. For up to a year. Any longer, and they'd get sued, there would be a Bosman like test case, and the whole system would get turned on its head. However, after a year or so, some team could come in, pay his compensation for him, register and play him. No-one does this, because they don't want to miss out on playing for a year, and the wages which come with it. They buckle down, and go next summer.
Why is all this important? This is why any player who kicks up a fuss, a-la Suarez, is almost always sold the next summer (if they still want to go) - because the clubs know they're pushing their luck regarding contract enforceability, and employment law (impeding opportunity etc). You can't make a player play for you, you can only sue them if they don't.
VVD and Coutinho are nailed on to move next summer if they still want to. Ignore any fan or pundit who chats shit about 'we've got him locked up for 5 years' - no, you have the right to compensation for 5 years, and a year after a transfer request, the club's power to really stop them turning out for another club has mostly evaporated in this game of legal chicken.