Steve,

thanks for your explanation. Apologies for taking so long to get back to you. 

My understanding is that the OSM map should reflect what's true on the ground as the first principle. I want to ensure that the map is both accurate to the user’s experience and respectful of the land management’s official policy. 

'Implicit permission' means that it isn't written down! The point being that because no attempt is being made to enforce the rules denying permission (over many years, and with many opportunities to do so) then the effect is to give permission. That might well not be the intent of the land owners, but it is the effect. 

access=no is too strong (in my opinion - reasonable people might disagree!), and the only next step down is to use access=permissive, informal=yes, and perhaps a note as to what's going on. That seems to me to make a map that really does represent the truth on the ground, while respecting the land owners official policy. 

Its a tricky situation but as it stands the map doesn't represent the real truth; it just represents the idealized one from the land owners perspective.  