OK there is something very odd going on.
I've got blog posts that I can see in the Database
BUT I cannot access them via their permalinks, nor do they appear on the Edit posts list. Well they DO if I start using filters - but the edit posts page only shows about 20 posts even though I have 40 and seems to have no way of paging through them
But if I access them via the old ?p=post_id permalink then suddenly their peramlinks start working again.