> I have a map from the 50s on my wall and the bus routes are the same, including numbers, as they are today

A surprising number of bus routes in Dublin still follow, to a large extent, tram routes laid out in the 1870s. And use the same numbers. This stuff is _sticky_ (partly because significantly redesigning an existing route tends to annoy people; there's a fairly strong tendency to just make a new one and leave the existing one running in some capacity).