The traffic road signs are good. It's the bicycle-path signs that are a bit odd. Often you cycle along, some armco barriers appear and you then realise a segregated foot/cycle path is running alongside the main road, but you can't get over the barrier. And the NSCR sometimes ends up in pretty steep offroad tracks, which are more mountain bike than touring bike; quite different to the NSCR in the other countries.
This problem of coming to a place where cycling is banned can usually be avoided by taking the road through a town or village, rather than the bypass road; or the minor road, rather than the main road (this may not be true in remote areas).
Cycling is sometimes banned through tunnels, on narrow bridges, and some dual carriageway sections. To be honest, I don't see any logic to it, except when it comes to something like an E road. That said, the route through a village may be the better option, anyway, but it's not always obvious on a map, because it may not look like a through route. Old through routes have often been blocked off to reduce motor vehicle permeability, but even where there is no through route for motor vehicles, there normally is for pedal cycles.
As for steep off-road tracks... they are everywhere. It's the nature of the landscape. Some of them are roads or converted roads. If my bike can't handle it, I just get off and walk for a bit. One route near me used to be the main road to Oslo, but it was closed to wagon traffic in the 18th century when a less steep route was built. It's still a right of way, and used by quite a few cyclists, but most walk up it and ride down. I only know one person who can ride all the way up.