Question about motorway tagging

In Greece a motorway has the name=Egnatia. Should all parts that belong to this motorway have the tag name=Egnatia? If so, ref=A2 is not visible anymore on the map but only the name Egnatia.

Thank you!

All parts should have the name. It’s up to the renderer to show both, if the developer thinks it is useful.
In Belgium many streets have a name and a national reference number, so it’s not uncommon to have both a name and a ref.

Thank you!

If the highway has a name, yes.