@Jurre: Do you want to assign an ecoregion to each of the sites and not only the priority places which are much larger? There are smaller and larger scale ecoregion from which you list the former. I think that the latter is better suited for our enterprise.
I was going to do it to the smaller ecoregions, but I started with the Priority regions, and now it seems to me that the priority regions in the first place, and the bigger ecoregions in the second place, are indeed better suited for our enterprise.
The smaller may be interesting for us, but are likely to be less suited for the exercise of the Top Missing 50. However, they may be handy (1) as background reading material and for understanding and (2) because the priority regions do not cover all these smaller ecoregions.
It's also handy as a tool to realize that we're talking about really large regions here, and that a bigger ecoregion comprises smaller ecoregions that sometimes are still bigger than most European countries. So sometimes, it doesn't feel right to say that an ecoregion is already represented with 1 or 2 sites, considering the vast territory the ecoregion spans.