After another visit to mid-Wales I've been able to fill in a number of new roads/tracks etc. There is still a lot missing, but its getting ever harder to plot routes between useful places via unmapped roads. When I first started mapping up there, only a few major roads were on the map, now its starting to look fairly complete outside of the towns and villages.
I think the next step will be to choose a village and do all the housing estates as thats the kind of thing that isn't easy to work into a route from A to B.
Gregynog is starting to look fairly complete, although there are still a few footpaths whose route is a bit of a mystery. They start of clearly signposted, but then the signs disappear along with any clearly marked track. I might move on to field boundaries on my next visit, as thats probably fairly easy to do.