Hybrid Game Styles?
I would suggest that rather than creating some sub-categories in some game-styles categories, it might be easier to identify certain players as employing 2 or 3 sub-categories in their games. Not enough to qualify as "true" all-court players but enough so that you can comfortably identify how the play.
For example, as dmastous correctly suggested, Annacone and Shriver (I might add Cash) would be classified: s & v/c & c
Edberg, McEnroe, Henman: s & v/net attacker
Rafter: s & v/net attacker/retriever
Sampras*: big server/s & v/net attacker/big fh baseliner
*Federer has caused me to re-think Sampras as a pure all-courter. Sampras was never willing to play defense and retrieve like Federer or Rafter and almost never drew opponents forward with short balls or drop-shots as Fed does regularly. While Sampras was more all-court than his contemporaries and predecessors, Federer simply utilizes more elements in his game than Pete did.
The same can be done with the other offensive and defensive baseline styles where a player combines elements.