I've heard about this one before, though I've never seen signs posted in street view (and I don't remember any specific to this one when I drove there in 2015, though I may have been going the wrong direction). Is it new?
There's also another Truck NY 25 in Greenport, using Moores Lane and North Road.
Some others we're missing:
-Truck NY 14 (Elmira): Clemens Center Parkway, Grand Central Avenue, McCanns Boulevard
-Truck NY 17C (Waverly): Broad Street Extension, William Donnelly Indus Parkway (not sure if this one counts; Bing streetside only shows "Truck Route" signs, not "Truck NY 17C" or "Truck Route NY 17C", but I've heard Region 9 refer to it as Truck NY 17C before)
-Truck NY 27 (Brooklyn): 10th Street, McDonald Avenue, Church Avenue
-Truck NY 32 (Glens Falls): Oakland Avenue
-Truck NY 340: William Street, Main Street
I believe there is a Bypass NY 125 in Scarsdale not in the system as well.
Regarding NY 25C, it was decommissioned a while ago and the signs seem to be erroneous. If it were to be added, it would bring up the question of why the signed reference routes (most notably NY 990V) aren't in the system.
There's been an issue on this in GitHub for a while. Ultimately, it comes down to the question of if the truck routes should be in the system. NYSDOT Main Office doesn't consider them official and has no inventory of them. They're signed by a mix of municipalities and the Regions and I'm not aware of an inventory at the regional level either. Signage isn't consistent either; while some are the traditional bannered "Truck NY (or US) XX", others are "Truck Route NY XX" (often the route number only appears on the first sign directing trucks on the route and the other turns and reassurance shields are simply "Truck Route") or simply "Truck Route".