[nvrspyx]

This is a good point in a general sense, but I don't think it would be a problem in this particular case for the date some imported OSM data was sourced, which is similar to the "date accessed" for a website in a bibliography.

[Archelaos]

I had the Open Historical Map sub-project in mind, which currently supports only ISO-8601.[1]

[1] https://wiki.openstreetmap.org/wiki/Open_Historical_Map/Tags...