In the 70s (see the Last Waltz DVD) Robbie had the middle moved to next to the lead pickup, had them wired in series for that overdriven sound he gets in the movie (he played a couple of 50s strats, one of which he had bronzed, in that show). If you can't see the middle pickup, I bet that's what he had done to this guitar.
The paint job (burst without the wood grain showing through in the center) and black pickguard/knobs color scheme seem to be something out of the 70s but the headstock is not the large 70s style.
Interesting guitar.