NIgel posted "IMO opinion, the first calc you do will be too low and the second will be vastly too high (distorted by someone bringing in their whole collection?)"

17 too low? I personally do not think that can be said across the board. I know of some detectorists who certainly find more recordable items than that. I also know of detectorists who find much less recordable items than that depending on their location - from zero finds which are deemed recordable to someone like myself who in nearly a year have had 5 items published on PAS with another 3 to be recorded shortly.

Norfolk has historically had a vast number of recorders who worked with the local units. The largest number of detectorists recording with PAS are in the County -The East region account for a third of total finds recorded.

There is no reliable way of calculating any figures for detectorists who do not record nor indeed the number of recordable finds they make. You are not talking apples and apples.