@Klumbumbus Thanks (especially for https://help.openstreetmap.org/questions/6368/in-josm-is-it-possible-to-see-gpx-track-waypoint-details - I’ll have a look at that later). https://help.openstreetmap.org/questions/26439/josm-validator-can-i-use-it-to-automatically-merge-duplicate-nodes is another “the accepted answer is that you can’t” one, and https://help.openstreetmap.org/questions/10622/josm-how-do-i-remove-commands-from-the-command-stack is really “accepted answer doesn’t actually work well enough to be useful”.