As explained in Spoke 1E, NCN12 is signed westbound from Clay Hill, even to the extent of a sign 3.2 over a stile as the LOOP path heads off NW into farmland en route to Hadley Wood. Eastbound, there is no such encouragement.
I suspect the long-term plan is for NCN12 to continue E on Waggon Road N of Hadley Wood and then a link track from Cockfosters Road to the LOOP path where it turns south for Trent Park. In wintry or wet conditions the path is not passable, and there are a couple of style porterages to negotiate, so we have to wait and hope this becomes an official cycleway.
For now, use Crescent East, Lancaster Ave, R 0.8 and L on Cockfosters Road, then Ferny Hill and Hadley Road. This is a busy deregulated road - hence the challenging classification, though it's a popular cycling route - until L at Oak Ave 2.9, meeting the LOOP (and NCN12 signs) again at 3 The Ridgeway. The final section is off-road along Rectory Farm Rd, meeting Spoke 1E at Strayfield Road 3.8.