Dot between “E” and “N” in “PENNY” not listed at Robson Lowe
Dave Burnett analysed at facebook:
It is possible that it is just a transient ink spot. As the stamp has oxidized, the normal color is orange, if you put the item in watermark fluid or lighter fluid, the ink colors, when the stamp is wet, should turn back to orange, if the dot does not, then I would think it is a trace of the cancel. Similar traces are showing next to the “N” of ONE and next to the “Y” of PENNY, as well as in other places on the stamp.