Tags on OSM are free-form. proposed:* tag prefix wiki page says the following:

" Proposed features that are not visible on the ground should therefore only be mapped in exceptional cases and after a discussion with the relevant OSM community, lest they might be deleted for lack of verifiability."

In general, proposed features are only mapped when it is certain that it will be there in the future, and the path is well-defined. Whether or not the trail was mapped by an organization has little bearing on this.