Council of Elrond

First Folk and The Necromancer are official DC sets.
A DC map exists, with many regions from unofficial sets.
So, in a First Folk/Necromancer tournament (like at Lure), a company cannot pass through these unofficial regions ?
For example, going from Taur Romen to Horse Plains by Sea of ​​Rhûn (to avoid wilderness) ?

Well,

there is a map, 2 maps actually, so I tend to say these regions can be used no problem

yours nicolai

Sure, you can use them.
As stated, though, all official new sites are located in standard regions or new regions adjacent to these. So unless you plan to take a needless detour, I believe your example of Sea of Rhun is the only one where it actually matters? You might circumvent Angmar/Gundabad by moving into the Northern Waste, but you'd need movement enhancers. Same for Belegaer. Misty Mountains is a mountain region so you cannot move through it (unless you have a Mountaineer).