It would be nice to have this clarified. The Midlands Mesh and Middle Road seem to be similar. It was my impression that:
You don't HAVE to use every control point, but you must check your distances by one of the normal (DIY) means. In many cases you could probably assume that certain legs will just add together e.g.
Tregaron-Llanwrtyd-Brecon = 30+34 = 64, because there are no shortcuts available,
but you must submit your route beforehand if you want to be sure.
So these meshes act as a handy guide for building good routes, or as a set of ready-made legs if you are prepared to control at every named point. (I confess I have stuck with DIYs, except where SteveA recommended a Middle Road route - and even then I had a very confusing conversation with poor Ross about this!)