Have we found every existing tactic? Is it possible that there are missing or unstudied tactics, waiting there to be found?

Maybe some of them have been played only by GMs and in so few times that they don't get to have a name on their own, maybe the rest of the world just see them as 'just another brilliant move'.

What I am saying is, if we were all geniuses and GMs, do you seriously think the number of known tactics would remain the same? Maybe they are so complex that they cannot be learned by books, but by experience.

Or, should I stop watching conspiracy movies?
The type of complex tactic you are thinking of is called a combination. A combination is a forcing series of moves to create some sort of advantage; some would also say that a combination must begin with a material sacrifice, but this is besides the main point. If you are interested in combinations, look at the games of Mikhail Tal, for one, who has been called "the wizard of combinations" for his daring, speculative sacrifices which often led to his opponent cracking under the pressure of searching out the one saving defensive resource; or Alekhine, "the genius of combinations", whose combinations, if not as daring as Tal's, were perhaps more sound.

Wikipedia gives the following example of a combination:

r1b2r2/p2p2kp/1pn1p3/8/1PP5/P2K1P2/2Q4P/R4B2 b - - 0 1

1... Rxf3+ 2. Ke4 (2. Ke2 Nd4+) (2. Kd2 Rf2+ 3. Be2 Rxe2+! Kxe2 Nd4+) d5+!! 3. cxd5 (3. Kxf3 Nd4+)  exd5+ 4. Kxd5 (4. Kxf3 Nd4+) Be6+ 5. Kd6 (5. Kxe6 Nd4+) (5. Kxc6 Rc8+) (5. Ke4 Bf5+) Rd8+ 6. Kc7 (6. Kxe6 Nd4+) (6. Kxc6 Rc8+) Rf7+ 7. Kxc6 Rc8+


In light of the impending disaster, White in fact resigned on move 3 (Move 22 in the actual game between G. Stepanov and Peter Romanovsky).