Because I made the stupendous discovery that some of the tracks aren't lined up between the old and new aerial images.
Unfortunately the nature of historical aerial imagery means that this is a risk. It's my regret that the process I used did not pick up that alignment issues were possible with the tracks in more than one or two places (the edges of the east and west ends of Addington).
Since this affects the middle part and every other part is aligned off it, this means I virtually have to start again from scratch with the middle part and then realign everything else off it.
I hope this won't take too long but the reality is that it could take another week. I will try to see if I can speed things up with two computers at once but I am not at all sure this could happen.