travellers wrote: but have come across a tiny flaw - there's no way for someone who's just upgraded to see what version he upgraded *from*!
travellers wrote:Still, it might be a sensible addition to the upgrade then, to have a visual indicator of the version upgraded from, just a short function underneath present version number which shows PREVIOUS version number.
This isn't hard to do - it is impossible. WP theme upgrades work by overwriting the existing theme folder. No developer has any control over this process, and there is simply no way to figure out what existed in a location prior to deleting it. WP doesn't keep track of the old version for several reasons, the simplest being that users could go into style.css and change the version number there manually, and then there would be no means for WP to determine what file got changed.
There may be plugins that provide such functionality in a rudimentary form, but you will always have unreliable methods to handle this.