Mihir Bose, BBC's sports editor tries to explain the Carlos Tevez saga and does a good job except when he mentions that the U18 rule is very obscure and cannot be applied to third party contracts.
I checked back on the PL ruling and Jane Purdon, the company secretary was aware of the law, except that she did not bother to inform WHU's legal director, Scott Duxbury, explicitly about that law. Mr Duxbury was advised by Ms Purdon against making private arrangements in a third party contract. The MSI arrangement was that they should be able to rent out Mascherano and Tevez on notice to other clubs.
Rule U18 "No club shall enter into a contract which enables any other party to that contract to acquire the ability materially to influence its policies or the performance of its teams in league matches or in any (other) competitions."
Granted it was written originally with a view to regulating single ownership of two clubs or more. The PL is very well aware of it but they make the case that third party contracts should be covered under this law, and no new one needs to be instituted. In a way it is a duopoly. The club has the playing rights but the private company owns the economic rights.
Simple case in point. When Alan Pardew was benching Tevez and Mashcherano, as his coaching call, was MSI sitting back and taking it? The number of appearances influence loans and transfer fees. That is why Masche was transfered to Liverpool for a higher fee which gave registration to the club.
WHU could not have railroaded this law. That is why they pleaded guilty and accepted the fine. In court, the penalty of point deductions would have been far worse. So the big question is whether you want to continue third party arrangements? Because there is clearly a law against it.