For me, the various comments and suppositions about this song demonstrate just how valuable Roud's approach, with its emphasis on evidence, is.

It is all to easy to jump from 'is believed to be', or 'might be' to 'is'.

Let us take the idea that a statue on one of the finials on Fyvie Castle represents Lammie, a character from the song. I wondered whether this would come up. The idea that it represents Andrew Lammie is complete speculation. Yet on one website, a claim that it represents Andrew Lammie is said to be 'irrefutable evidence' that the story is true.

There are six such statues, and their significance is discussed on page 136/137 of an archaeological report on the castle.

https://www.euppublishing.com/doi/pdfplus/10.3366/arch.2015.0071

Let us take the gravestone of Agnes/Annie Smith: it is hard to find an account of what it says, but no account of it I have found states that she was murdered, the fate provided for her in several versions of the song.

My garden exists, but this does not mean that there are fairies at the bottom of it.

Otherwise, toys, pram etc.