Wills are rarer than writs. The first dedicated study, "Anglo-Saxon Wills" by Dorothy Whitelock was able to identify 39 documents. The number grew to 55 with publication of another 16 among the "Anglo-Saxon Charters" by Agnes Jane Robertson in 1939. Since 1939, contributions to the list were few and far between; in her 2011 "Wills and Will-making in Anglo-Saxon England" Linda Tollerton published the most up-to-date corpus, with 68 examples in total. The surviving documents are very unevenly distributed both in time and space: from the 9th century, for example, only 9 wills are known, and 6 of them are in Canterbury. Not a single will from any period is known from further North than Burton upon Trent in Staffordshire. Furthermore, only 22 wills can be found in manuscripts written before 1066; originals are even rarer, as some, like those of Alfred the Great or Wulfric Spot, are known to be pre-Conquest copies, while still other may in fact be mere extracts or ancient forgeries.