For a number of years I have sporadically looked to resolve missing speed limits on major highways (highway=trunk and highway=primary) in the UK. I use a simple Overpass query to find these in a manageable area (usually former regions of England + Wales, Scotland and Northern Ireland.
The other day a discussion arose on IRC about some distinctly English placenames in North Wales. Looking at the area I realised that the A493 had no speed limits added. As both Mapillary and now Bing Streetside imagery are now available in the iD editor, I was able to add limits from Aberdyfi to Tywyn. In the past this nearly always required a survey.
I was going to write about looking at limits elsewhere, but found it easier to add various pictures in a short Mastodon thread.
tl;dr: There’s lots of work everywhere to improve the mapping of maxspeed on highway=primary.