PANS-ATM says (my bold)....
4.5.7.1 CLEARANCE LIMIT
4.5.7.1.1 A clearance limit shall be described by specifying the name of the appropriate significant point, or aerodrome, or controlled airspace boundary.
4.5.7.1.2 When prior coordination has been effected with units under whose control the aircraft will subsequently come, or if there is reasonable assurance that it can be effected a reasonable time prior to their assumption of control, the clearance limit shall be the destination aerodrome or, if not practicable, an appropriate intermediate point, and coordination shall be expedited so that a clearance to the destination aerodrome may be issued as soon as possible.
4.5.7.1.3 If an aircraft has been cleared to an intermediate point in adjacent controlled airspace, the appropriate ATC unit will then be responsible for issuing, as soon as practicable, an amended clearance to the destination aerodrome.
4.5.7.1.4 When the destination aerodrome is outside controlled airspace, the ATC unit responsible for the last controlled airspace through which an aircraft will pass shall issue the appropriate clearance for flight to the limit of that
controlled airspace.
It goes on...
4.5.7.2 ROUTE OF FLIGHT
4.5.7.2.1 The route of flight shall be detailed in each clearance when deemed necessary. The phrase “cleared via flight planned route” may be used to describe any route or portion thereof, provided the route or portion thereof is
identical to that filed in the flight plan and sufficient routing details are given to definitely establish the aircraft on its route.
So number 1 is a valid clearance provided that there is no doubt about the flightplan details - Blocka and cossack describe some of the problems with that simple proviso. And the problems will probably only increase as some of the changes to flightplan procedures and details coming into European legislation are implemented. Concepts like preferred business trajectories are good in principle but cannot easily be mixed with 'old' systems.
Number 2 is also valid but, I suggest, usually is adding unnecessary complexity.
Number 3 is ambiguous in my view with two apparent clearance limits and so is not valid.