I have read the Wikipedia rules a few times and  As far as I can find it says All reliable sources are by definition both published and accessible to at least some people Sources that are not published eg something someone said to you personally or not accessible eg the only remaining copy of the book is locked in a vault with no one allowed to read it are never acceptable as sources on Wikipedia In my interpretation I can refer to  Jahre Handel und Kultur im Ostseegebiet  Gotland Perle der Ostsee ISBN As far as I can see this book qualifies If you accept this we can go further If you search ISBN on Google you will get  results  OpenFuture does not accept this Are you reading the rules in the same way