More recent information shows that the Morris Mini Minor (ie: the 850 with the wind-up windows) was introduced in October or November 1965 - see below image of driver's handbook for car number YMA2S3 562, sold new to NSW Police on 8 November 1965.
These used the same Australian-pressed body panels as the Mini De Luxe, hence the same doors with wind-up windows, but retained the dry cone suspension and the "pudding stirrer" gear selector of the 850. Between January 1966 and January 1969 there were reportedly 2,248 Mini Minors built.
As you can see, car numbers reverted to 501 with the new model, as would be expected, so numbers on all these cars should be quite low.
It is likely that this late introduction, some 7 months after the introduction of the Mini De Luxe, was due to remaining sliding-window body shells being used up in 850 production. It is not likely (though you can't discount all sorts of silly decisions from BMC) that there would have been sliding-window 850s and wind-up window 850s available at the same time, even for special orders from PMG, etc, due to the unviable nature of such production. BMC Australia at that time seemed to be pretty switched on and was at its most profitable period, with the Mini at its sales peak.
And can you please check out your dead one's as well, there might be one there.
