Regarding this section from the border to Maribor, I'm going to opt to add the EV9 ref - the Eurovelo site says it's signed, and I'm going to use that as my source of truth.

It's also interesting that this section is mapped "D-1", whereas the rest of the country (and indeed the rest of D(-)1) seems to be mapped without the "-".

For some additional context, here's the sign mentioned on https://www.openstreetmap.org/relation/193490#map=12/46.6272/15.6580&layers=C: https://maps.app.goo.gl/qgHNmBJ9WpGETdZX6

This is given extra weight by the apparent mapping of EV9 from Maribor to Slovenska Bistrica. I would be interested to know how this route was picked, since it doesn't seem to follow the Eurovelo site (which says that the route is undecided).