Question: I run joplin on 4 devices, synced between them through dropbox. I image each device about once a month.
If I need to restore a device image, using a perhaps 3 weeks old image, will old joplin data get synced to all devices, overwriting current data?
When imaging on the client side (Joplin on each device) data will not be overwritten on the server if you restore an image on the client side, providing it is genuine image restoration which does not alter file timestamps. It will just download the latest changes from the server when you sync.