Those who think that the Barton letters are just reasonable "oversight" should have a read of what Professor Hans von Storch says, towards the bottom of this news article. von Storch has previously been outspoken in his criticism of Mann, calling his work "rubbish."
I don't know of any scientist who could answer such questions. It's just not the way our work is done - there is far too much pressure for rapid and new results for us to maintain full "audit trails" and answer an unlimited number of questions from any troublemaker with too much time on their hands. By the time 5 years have passed, our work is either irrelevant and forgotten, or else superceded, either because it really was wrong, or because someone else improved on it. In either case, complete replication of the original is a waste of time.