I would vouch for differences in roadsign fonts ,with newer signs being heavier (bold). Same font, but appears different.
Wonder if now they are digitally printed, whilst the older ones would have been laid up by hand.
Ireland uses 100 km/hr signs instead of the national speed limit sash. Which to me in a world of speed sign recognition on cars makes sense. I know that means that the 10 mph drop for vans and trailers gets killed, but not many vans heed slower limits anyway.
And I guess I am one of the few on the board to hanker for complete 'metricification' in uk.