I wonder if the cessation of striking the currency 10p had anything to do with the continued use of the old florins? 1981 was just after the silver bubble, and although the silver price was still above face value, the collapse of prices in 1981 must have freed up a quantity of Cu-Ni pieces initially retained in the belief they were silver, not to mention bags of deposited florins previously obtained from the bank to sort through for silver. You still get predecimal Cu-Ni saved in the belief it is silver today, so not a lot has changed as far as the man in the street is concerned.
The same pattern exists for the 5p, with the next currency issue being in 1987. The 50p by contrast was issued approx every other year