Hello miluethi,
Thank for you all of your insight and perspectives on how you’ve modeled these refs. I believe it would be better if the refs across the country consistently followed the same pattern.  With Nicaragua's two distinct route classes (NIC-##  for the main roads and NN-### for smaller routes), the prefix is useful information. I think the larger issue, more than consistency or utility, is that this method of modeling refs goes against the two OSM best practices of ‘don’t map for the renderer’ and ‘map what’s on the ground’ (https://wiki.openstreetmap.org/wiki/Good_practice). Tagging the route relations and ways in different ways could lead newer or more inexperienced mappers to remove or alter the ref tags on the relations and/or ways when attempting to follow global OSM best practices or ref modeling policy which specifically states that refs should follow what’s on the ground (https://wiki.openstreetmap.org/wiki/Key:ref#Examples_on_ways). Most of the refs on ways across the country still have NIC-## or NN-### on them, but after these changes the ref system is now inconsistent across the country.

All of that being said, though, the Apple team is committed to following local mapping practices and preferences whatever those may be. I believe that the best way of going about making these changes to Nicaragua’s ref system would be: proposing the widespread removal of ref prefixes (NIC / NN) to the larger Nicaraguan OSM community, getting a consensus to agree on those changes, and then documenting the country-specific ref tagging method on the OSM Wiki. Otherwise, unaware mappers attempting to follow global best practices may overwrite your edits and create a more inconsistent map of Nicaragua for everyone. If you would like to have a more open ended discussion about ref tagging with the broader Nicaraguan OSM community or would like assistance with proposing, updating, and implementing country specific tagging guidelines, I can get you in touch with our community manager Teddy. Without local consensus, though, I think it would be best to return the ref tags to how they were modeled before. Let me know what you think and if that works for you!
Thanks and Happy mapping!