Box found High Dartmoor Snowdon Brook page 602

I was letterboxing today in the Whistman's Wood area walking a charity route and came across an old stamp "High Dartmoor - Snowdon Brook - Page 602". I took a print of the stamp but cannot find any reference to this in the two books that I have from 2014 and 2009. I would like to know the registration number for this stamp. Some "High Dartmoor" stamps are still in the books. Is there a way of contacting the owner?
Yours
Mark
[email protected]

Hi
This was a huge series back I the day. I collected loads of them. I think it was Pebbles who put them out, all word of mouth. She doesn't any more though is my understanding. This one seems out of place at Whistmans wood, but I don't have it. Shame, im heading up there soon Id love to get it as they are so scarce these days.

The High Dartmoor - Snowdon Brook letterbox is one of a series, put out as a walk in the Two Bridges area. The series was original put out by Pebbles & Co., who retired from letterboxing. The remaining unissued stamps were acquired by The Hand Of Man who then sited them on the moor.
It seems that I can only post on this Forum by using Microsoft Explorer and once logged in, preview my post before I can submit it. All very tedious and annoying as this is my eighth attempt today to post the reply. Will try the same 'preview before posting' method and see if that works on Microsoft Edge.