This probably has been discussed before, the Nash post is from 2013, but as a friend of mine just asked me about Spence, I found this on a search and hope to get some reaction from the experts here. Nash's research as always seems meticulous but I am aware of his reputation. If Spence truly has made so many major mistakes, how meaningful can his authentication be?
http://haulsofshame.com/blog/?p=26228