Sorry to be a bit negative here.
Two years ago in a rash moment, I took it upon myself, not merely to cycle up to London for a CM, but also to try and pick my way along a NCN (no. 23 I think it was) as it wended its way north from Croydon through Crystal Palace, Dulwich, etc.
I failed. I missed a turn and got hopelessly lost. Eventually I found myself emerging on one of the main arterials into central London, and was still able to make CM on time. In spite of, and no thanks to, NCN. On all subsequent rides north from Croydon, I've simply gone straight up the A23.
I blamed poor signage. The maps I had on me were simply not detailed enough. If one turn sign for a NCN is absent, and you don't know the area, you will lose the NCN, and no amount of subsequent correct signage will make up for it.
So it looks like, the work you're putting in is most welcome and not before time! If this situation has been, or is being addressed, well and good. Hopefully I'll then be able to be more positive about the NCNs.