How to combine multiple regions properly?

Communities Österreich (Austria)
1

I want to add the official classification for nuts to OSM NUTS:AT – Wikipedia.
Nuts is closely linked to existing regions.
Eg. AT335 Tiroler Unterland consists of 3 existing relations.
Is the correct approach to add the paths from the existing Regions in the new Relation? Is there a way to get the outer boarders of multiple regions? (I started with JOSM and Overpass).

For tagging the new Relation I used these tags:
ref:nuts:3=AT331
ref:nuts:3:name=Tiroler Oberland
region=NUTS-3
region:type=natural_area

Is there a better more recommended way?
Reasoning:
A) ref:nuts:3:name → The nuts nomenclature is sometimes identical to existing OSM Relations but the name is deverging eg. sometimes the name is in the alt_name and sometimes completely different. To get a proper resultset if I’m querying it later I can use ref:nuts:3:name with the correct nuts names.
B) region=NUTS-3 is used because some people already started tagging nodes (cities) with ref:nuts:3 which makes sense in a way but to be able to properly select the regions in one simple query it needs this marker.

2

Ich würde mich beim Erfassen an bereits bestehenden NUT-Relationen orientieren - z.B. Westösterreich oder Leipzig.

Analog dazu würde das Tagging für das “Tiroler Unterland” dann so aussehen:

type=boundary
boundary=statistical
name=Tiroler Unterland
ref:nuts=AT335
ref:nuts:3=AT335