The tune, as Graham Pirt mentioned back when this thread was young, is very old and very widespread; most often heard attached, nowadays, to nursery rhymes (Baby Bunting for one) and playground taunts. A. L. Lloyd frequently pointed this out, together with its association with ceremonial customs. It is not the only tune used for souling songs; in some cases tunes and texts have been borrowed from wassail songs.

The earliest published examples of tunes are, so far as I know, a set from Tattenhall (Cheshire), included in Lucy Broadwood's English County Songs (1893) one from Eccleshall (Shropshire) in C. S. Burne's Shropshire Folk-Lore (1883) and one from Mobberley in R. Holland's Glossary of Words used in the County of Chester (1886). The first is the minor trichordal melody made popular in the Revival; the second is similar, but in the major; and the third is a borrowed wassail tune.

Certainly soul-caking is an old custom, but attempts to date it to the 10th century seem to be based solely on the fact that the festival of All Souls' Day was instituted in AD 993, and are probably no more than wishful thinking. Most such customs are little mentioned (if at all) before the 18th century, when there was an upsurge of interest in antiquarian subjects. It seems reasonable to suppose that there was a form of the song current for some time before it was first noted, but we have no way of telling how long. The fact that the tune is old tells us nothing about the song.