I think you may be wrong Jabberwock.
There are special arrangements in place for the Isle of Man. How else could Manx Airlines have held its own AOC being resident on the Island? A new AOC was issued for Manx Airlines Europe (which was re-named BRAL) when they started to operate from the uk.
The Manx aircraft registry is quite different and does not pretend to regulate public transport operations. Jet2 could, therefore obtain an AOC should it wish as could have Manx Europe. The fact that they donīt is purely a company issue unless the rules have recently changed.