Bulk of the enamel caries starts at the contact area which is clean. The acids from fermentation of food can reach the contact area but the saliva and biofilm cannot reach the contact area. There is no difference between the deciduous teeth and permanent teeth. I am sure no body will treat the permanent teeth like this. Bulk of the enamel caries starts at the edge of the plaque and contact area is located at the edge of the plaque or biofilm.
NRCT is not a feasible option for teeth inflicted with caries, as the nonrestored area would cause food impaction or the growth of gingival polyps which could worsen the situation. Thus all carious teeth have to be restored.