I haven't followed the "which ELT for which country in Europe" closely but vaguely recall someone discovering that the regs which mandate a fixed 406MHz unit apply only to planes whose CofA was first issued after about 2008.
I think the problem is that the word FIRST doesn't appear in the Dutch regs. Also the part about C of A only relates to auto activation units. See the first post on this thread for a link to the document.