Half a dozen points to consider regarding legitimacy:
Not a Footpath
Not a Bridleway
Not a Restricted Byway
No Access Only or No Entry restrictions are signposted
From Norden cross the first 10 yards or so is on the List of Streets
There is no access to property from the lane so it cannot be claimed to be a private access way
From Denbury the way this leads to is known as Denbury Down ROAD and the public have access to the hill fort, and this way is recorded in the same way, albeit without the benefit of a name which is not unusual
So since we are not prohibited from using it for the reasons listed above and since DCC have consistently refused to confirm that being on the List of Streets affirms legitimacy, and because it will be helpful in the future to have user evidence to back up our claim should it's status be called into question.
The question that springs to mind is not "Is it legit?" (certainly not illegal, see above)
but "Why should we not use it?"
PS: You would probably struggle to prove you have a right to drive down the road upon which you live unless it is recorded on the Definitive Map as a Byway Open To All Traffic or you own the land
I guessed that i don't know how often it gets updated?....
The overlays are updated frequently but not automatically distributed - you have to ask for them and even then they're only available to current TRF members.
The regular updates could be additions of new lanes, downgrading or TROs on existing ones or descriptions changed to more reflect changing characteristics: what was easy last year may be a trials section this and vice-versa - the run sheets are a vital feed-back mechanism for maintaining accurate lane descriptions. So, it's in your interests (and that of Devon TRF) to be using the latest overlays.
A word of caution though... The Claim Lanes Overlay is provided for information only and are NOT sanctioned for use so you 'ride at your own risk'. They're lanes we believe we have sufficient evidence to counter a prosecution for riding but I'm sure nobody here would want to be the subject of a test case. That said, if you should ride them then a run sheet is an important addition to the evidence we hold.