To get back to the initial question, Walker's dates were 1830-1941, Peter Buchan 1790-1854, William Christie c.1817-1885. Walker, who began his interest in folksong late in life, makes no mention of having met either Buchan or Christie (who only started collecting from 1844 onwards), but points out that Buchan's versions were confirmed later by Christie's.

As Mary Ellen Brown's "Bedesman and the Hodbearer" ably shows, Walker only advised Child towards the end of Child's publication of the great English and Scottish Popular Ballads (1888-1892), and did no 'legwork' or such.

Although, in his understandable admiration of Child, Walker fell in politely with Child's dismissive view of Buchan, he was to recant completely and publish his detailed defence in "Peter Buchan and other Papers" (Aberdeen, 1915), a defence strongly supported by both Gavin Greig and James Bruce Duncan, major collectors who also knew the North-East of Scotland's song and ballad tradition intimately.

Walker's high opinion of Buchan and his findings? Walker was in fact bitterly opposed to 'trash' of any sort in folksong and was unhappy that Greig and Duncan's motto was (uniquely for the time) "Give exactly what you get" from their sources, for their collection thus included music-hall songs, popular street songs, slip songs of ballad hawkers, and other rubbish he considered 'not true folksong at all'. So bitter that after their early deaths (1914: 1917), Walker only permitted the great Child Ballads in their collection (only 13% of the whole) to be published as "Last Leaves" in 1925 (introduced, by the way with an able defence of Buchan). All this is in the Oxford Dictionary of National Biography entry for Walker. If Jack Campin has difficulty accessing that, much of the detail appears in the entries I also supplied for 'Gavin Greig' and 'James Bruce Duncan' in the final volume 8 of the Greig-Duncan Folk Song Collection (2002).

P.S. Buchan's "mss" only publisher's proofs? I am surprised that the usually thorough Steve Gardham has not seen the British Library's unpublished Mss of Buchan's. I reproduce the title page of these handwritten mss on page 158, of "'The Bonny Lass o' Fyvie or 'Pretty Peggy of Derby'", in the recent Review of Scottish Culture, 22 (2010) 150-163. This paper also reprints the superb 24-stanza version of 'The Bonny Lass o' Fyvie' that Buchan collected, typical of the quality of his material (Malcolm Taylor in the Vaughan Williams Memorial Library has offprints of the paper if anyone is interested).