Technically Doc would be the only one going "back to" the future in that case. It was Marty's first time going.
No Mutants Allowed
Big No
Richwizard
Lack of imagination. Also, they filmed 2 and 3 together. Might have looked awkward with "Back 2 the Future" followed by "Back 3 the Future."
Walpknut
Back to the Future³
Richwizard
See? It's all about imagination. Modern film makers don't have enough, in spite of what they try to make us believe.