Martin, are you sure about that? My recollection is that if you have a version that’s older than what the documented upgrade path allows, the ZD will let you waste 5-10 minutes uploading the image and then it will tell you that the image is invalid, not supported, or something like that. At that point the only thing you can do is abort or cancel.
Regarding factory resets - I’ve never seen a ZD do a factory reset when upgrading. As I recall, the only time the ZD will factory reset is when downgrading to an older version that is missing features contained in the release currently on the ZD.