Okay a quick and simple analysis of the sources stanza by stanza.
1-5 paraphrase 'Outlandish knight'.
6 is found only in A and continental versions whence Buchan took it.
7-11 are all derived from Buchan's B version. (The irony is that Buchan has been Buchanised!)
12-14 paraphrase 'Outlandish Knight'.

Now if we can find a composite from say 1850 that matches then fair enough, 25 years from print to oral is nothing, but if not then Scarborough herself comes under strong suspicion!