This group is certainly the choir, I've really only had trouble momentarily finding the trail when starting before sunrise in hardwood forests after all the leaves have come down. The leaves cover the obvious footpath and if it's a busy trail, blazes may be spread out as in normal summer conditions in the light, the trail is obvious. (My first time up Windham High Peak from the back, in the dark, early December, no snow)
Relocations occur, side trails to brooks and vistas can turn people away. When the snow flies, we change the trails too. Valley Way in some years misses the turn near treeline and continues to the hut in the drainage, bad early and late but no issue in mid-winter. The upper section of Ammo isn't followed that well in winter and some have lost the trail at Gem Pool, as the more open option is along the water not up the narrower opening of the trail.
Some trails have junctions with narrower trails and are at hard angles. Mizpah Cut-off near teh but is easy to miss in the dark or rain. The South loop of the Shenipsit Connector in CT was relocated and the old trail is still very visible and not blocked as roadside parking continues to use the old trail to access the trail and avoid walking on the road. In some state lands, Gas lines are buried underground but the ROW is kept clear. (Similar to picking up the Huntington Ravine Trail when it crosses the tote road up to the Cabin. Any place with recent or current logging will have logging roads make things harder also.