Isn't the point of Fabricated claims that you just go and dig up the local families histories and say that "this land used to belong to such and such a title; it should be part of their, and hence my, realm" or something? Whereas this kind of claim is just some bloke saying "I declare myself king of all France/Iberia/England/etc". I'm not sure that the fabricated claims are any less legitimate.
I like the idea of permanent claims, but they shouldn't be stronger than any other [pretense for taking] / [legitimate right to rule] someone else's land.
Now I'm just guessing, but I got a feeling that the whole "fabricate claim" concept is pretty much based on Louis' XIV
Chambers of Reunion.
Read about it here:
https://en.wikipedia.org/wiki/Chambers_of_Reunion
This corresponds to your first example and these types of claims where considered pretty
weak.
However, the "I declare myself king of all France/Iberia/England/etc" is another story, because that is a claim of overlordship based on currently holding a title with overlordship over a country, not some ancient document. This is a stronger claim, even if most often respected only in theory by those concerned by it - if the claimant didn't have the muscle to enforce it.
A good example of this would be the Burgundian Inheritance. How come Austria only took the Lowlands and the Imperial part of Burgundy and not the actual Duchy of Burgundy itself?
Because the Ducal lands were offically within the borders of the kingdom of France and it was an appanage, meaning that the rules said it must revert to the crown should the male line become extinct. The French king thus had a strong case legally to deny the Habsburgs this Duchy and he had the military strength to enforce the claim in practice, a claim which must be considered stronger than any fabricated one.
A interesting twist could be to introduce a new diplomatic action, where you can
demand fealty from independent tags that are nominally your subjects, if they refuse you receive this permanent claim. Though I would like to see diplo-annexations becoming much harder (ie, vassals regularly resisting such an action by seeking support from the overlord's rivals), but that's a totally different topic.
