If you are speaking in terms of "variants" (as I seem to get from your question) I would say always pretty inconsistent, as all these cover variants are niche books at best.
On the contrary, if you are looking at foreign editions on an historical perspective, you can manage to have a clearer vision of each country’s market, as the collecting habits are very different.
Even with his inconsistencies, for example, the italian market has more or less values upon which one can make his judgements. Keep in mind that outside USA for most people a VF/VF+ and a NM are more or less the same thing.