Doug- All the greens were much smaller pre 1870, mainly they were the middle areas of the current doubles. As there was more play, came the need for wider fairways to accomadate outgoing and incoming play, the greens wideneded some by many times their original size, its possible even the 17th was smaller as a double pre 1870. When TM built the new 1st and developed the routing we know of today, the 17th as a double green no longer existed, so would not have been extended in the same way the others were. From 1870 St. Andrews was almost a new course with the widened routing, there could be a lot of reason to credit Old Tom as the architect.
A few other points that may or not be true. (I was told this via one of the Aytons's)
I think the reverse route that was used 100 years ago did not play to the 1st green or to the 6th green, ie the current 17th and the current 12th played over shared fairway, the area to the left was very heathery.
I read once that the 1885 Open championship was played over the reverse route.