Interestingly, there's 10 on Richard's rare penny list (including this one), and of that 10, six are more or less washers. So if you see one for sale, it's more probable than not it will be a clear date washer, and you're going to have to pay.
In his book "The British Bronze Penny 1860 to 1901", Gouby said there were 15 known in his 2009 pricing and rarity pages. But at page 48 of his 2020 amendments, he says there are 8+ known.