Hello,
DN, DJ, DC are part of the official name/ref of the road and signify the institution that administrates the road.
DN=Drum Național (national road)=administered by the national road company
DJ=Drum Județean (county road)=administered by the county council
DC=Drum Comunal (municipality road)=administered by the local municipality
The name/ref of the road is official and we cannot simply change DJ to DN on the map.
Also the official name and the importance of the road are not necessary matching, it is given as a guideline on multiple OSM pages, but we practice in Romania the highway=* classification based on relative importance of the road. While the road has been build by the county council it is still of primary importance, it is an high traffic ring road of Oradea. 
The unusual DJIMO ref means "Drum Județean Inelul Metropolitan Oradea" - "County Road Oradea Metropolitan Ring Road" and is seen on roadside traffic signs as you can see for example in the following picture from the local press: https://www.ebihoreanul.ro/modules/news/files/inelul-metropolitan-rutier-deschis-foto-cj-bihor-28062025_03.jpg