iD already displays labels in the form “network ref directionbound from from to to via via”. This format is localizable and may differ slightly in other languages. Do users need the punctuation to match the proposed formula specifically for this one network, or would the existing format suffice?
Currently, iD only generates this label if there isn’t already an explicit name, based on the assumption that a name is already specific enough for the user to roughly identify the relation, even if it isn’t unique among relations in the area.
It looks like you’re all taking on a lot of issues at once. As someone from halfway around the world, I wouldn’t want to scope-creep this effort for something as pedantic as ref formatting, especially if the community is open to refining tags in the future.
For what it’s worth, I do think it’s worth distinguishing between the “core” part of the route number and the overall abbreviation that refers to the route. This enables data consumers to do more with ref than if the value bakes certain assumptions in. The calculus is quite different from way refs, because network normally doesn’t get tagged on ways, and way refs aren’t necessarily machine-readable anyways.
In this case, is it appropriate to call the route “EuroVelo EV17”, or is it just “EuroVelo 17”? If a renderer wants to display a heavily simplified shield for the route due to space constraints, would “17” in a blue rectangle be misleading? If you expect data consumers to include the “EV” prefix in some contexts but not others, then I think it should be omitted from ref so that data consumers can decide to prepend it when appropriate.