Hi Rob and thanks for your reply. I wish i knew about this forum before now.
This is a coin i sold about 2 years ago as a1698/7 overdate. The buyer was in a bit of a dispute with me, which we sorted, with him stating that it should be a Septimus edge and not a Decimus edge. It is an overdate as you say and listed as extremely rare. I have another on sale which is listed at DNW auctions next month, which they valued by pictures, giving me an estimate of between £800-£1200. But on inspection, again it was a Decimus edge. So the value went down down to between £300-£400 because of this. I.m still happy with the price as i picked it up at bargain basement price. They are both the same overdates and both extremely rare, do you think the price difference has something to do with mintage numbers?