A few other related tidbits: 1) Crawford 2008 cites the Old Parochial Registers of Scotland as listing a Robert Turnbull as "witness" (to the baptism, I suppose), so there's the source of the name  whoever Robert Turnbull was. 2) Crawford 2008 also claims that Robert Turnbull Macpherson disappears from the records of the Royal Scottish Academy's exhibitions after 1839, while Robert (T) Macpherson appears in Rome in 1840. Part of the significant, but still circumstantial, body of evidence that the two are the same person. IainL, you said "We have been advised elsewhere not to correspond with Alistair Crawford". Can you elaborate? In my correspondence I found Crawford to be most helpful.