flapper - the main reason John is authoring the book is so questions like these can be answered. I think he'd be keen to help.
This is an example where parts books don't show the change point, unfortunately. I'm aware of many production changes to the Mini where the detail wasn't reflected in a parts book, and especially towards the end of a model's run when attention was being directed to the new model. For example, the MK II Cooper S parts book makes no mention of an alternator being fitted, only a generator.
The photo below is courtesy of miniresto on here. The Morris 850 on the left is a 1964 model with UK boot lid pressing. The one on the right is late 1964 or early 1965 and shows the Australian boot pressing that we think came into production in May 1964. You'll see both have sliding windows so a change to wind-up windows didn't happen at the same time as other body panels adopted the Australian pressing.
Mini Series parts list PUB1012 (below) issued in 1969 shows different doors for the Morris 850 Saloon and Van, and Morris Cooper versus the Mini Minor, De Luxe, Matic and Cooper S. The HYA part number prefix means an Australian part.
Finally, page 55 of Issue #5 of The Mini Experience has an Australian Mini timeline that includes the following:
1965- March - Mini De Luxe released with wind-up windows
- May - Mini van gets wind-up windows
- Oct - Morris 850 gets wind-up windows - name changed to Morris Mini Minor
So I guess it depends on whether the car in question is badged Morris 850 or Morris Mini Minor. If the former then it appears it always had sliding window doors.
Hope that helps in answering your question.
Attachment:
JH Morris 850's.jpg
Attachment:
PUB1012 page RC2-1.jpg