Hi Piedmont Park.

This is a really good question and there is no perfect answer to it. 

The short answer is that ref-tags should be as short as possible to avoid rendering issues.

The longer answer:
For all highways with an updated ref-tag, I created a relation=route and with a name=NIC-xx and a ref=xx. So you still can search for the "NIC-xx" feature and the road name shows NIC-xx, but the road banner is only "xx"

The the official documentation for the road network in Nicaragua is the Red Vial Nacional 2020 by the MTI here: https://biblioteca.mti.gob.ni/ and it lists two types of names NIC-xx mostly for the main roads and NN-yyy for mostly small roads. There is no case where NIC's and NN's share the same number. So the number is unique within the entire Nicaragua.

On official INETER maps, the roads normally have only a number --> Google search "condega-nicaragua-50k-2956iii-1986". This map shows NIC-1 as "1" and NIC-51 as "51"

Adding NIC- or NN- to the banner road number makes it the harder for OSM to render correctly, to read and doesn't help to identify the road.

I created also relation=route together with shortening the ref tags. If the community decides to move to add NIC-xx and NN-yyy this can be very easily done.

Historically, most of the NIC and NN road names were introduce by myself in 2012-2015 when I lived in Nicaragua ;-)

Let me know what you think ;-)

