The following note, appended to the DT version of "All Round My Hat I will wear the green willow",

"Recorded by Steeleye Span on All Around My Hat.
Note: This hit the pop charts in England in 1975 and made
the Top Five, the highest chart placing ever for a traditional song. MJ"

is about as wrong as it could be.

No it is not.

Whatever you might personally think about Steeleye Span's version of "All Around My Hat", the note at the bottom of that particular entry in the DT is correct as the song given above it is the one recorded by Steeleye Span.

That it is, as you say, a chorus from one song with the verses from another is correct and you could argue the case for a note to this effect about Steeleye Span's version, but the note at the bottom of that particular DT entry is correct as far as it goes.

You are also incorrect in saying it is appended to the DT version of "All around my hat I will wear the green willow", it is appended to the DT entry for "All Around My Hat". The DT entry for "All Around My Hat (I will wear the green willow)" is the one for the original song and does not contain the note about Steeleye Span's recording.