For what it's worth, I do not think this is a very rare thick flan 10+J but rather a normal flan one where the rim has been "rolled" in machinery and slightly compressed thus, and so makes the edge look wider. My evidence for this is
a) this was commonly done with many, many bronze predecimal coins, I guess as people were just playing around with lathes etc in workshops, and I personally have many such examples of all bronze denominations and several monarchs, and
b) from your photo, the rim itself next to the beads appears to be thin or non-existent, when in reality there should be a distinct rim edge surrounding the beads (see photo of obverse 10 below, taken from Richard's halfpenny website) which is basically where the rolled metal has gone from to form the "thicker" edge.
c) The genuine thick flan is R20 for rarity, so VERY few known indeed. Of course, that is not to say another one wouldn't ever turn up, but mathematically one is more likely to find further specimens in the R17-R18 bracket, as you proved with your 1877 narrow date.
But of course, one can only be sure when in hand and can be weighed, measured etc. But if you ask opinions from vague photos, be prepared to get vague answers, or indeed an absence of answers in light of the absence of evidence!
I wish you luck with this purchase, just as you have had much luck already, but equally you must expect disappointments too... Also, give things a bit more time for feedback: you only posted on Saturday morning - I am replying Monday afternoon!