I found the piste:grooming description from the ‘Piste maps’ (osm.wiki/Piste_Maps#Grooming) or the Key:piste:grooming (osm.wiki/Key:piste:grooming) pages that was derived from the earlier not very clear. I’ve made an attempt to re-write it to document actual usage here:

osm.wiki/Talk:Key:piste:grooming#Page_rewrite_proposal

I’d like to have some comments if you think I missed something. This is about actual usage and better comprehension. If the values re-used from one type of piste to another does not suits you, it’s another story that can be dealt with later.

Yves