3872)   YOUTH'S THE SEASON  From John Gay's Beggar's Opera (song number XXII, though the DT file does not say so).  Frank Kidson (The Beggar's Opera: Its Predecessors and Successors, 1922) identifies the tune to which it was set as follows:
"Air: Cotillon. This is a French cotillon called Zoney's Rant, in the third volume of the Dancing Master (circ. 1726)."
Midi made from the notation in that book, found at Robert M. Keller's  The Dancing Master, 1651-1728: An Illustrated Compendium  where it is given as Toney's Rant.  I don't know which is the correct reading; it is impossible to tell from the image file.

1177)   FLY UP, MY COCK (2)  There is a note in the DT file saying, "from Sam Henry's Songs of the People where it's called The Bonny Bushes Bright".  Seems not the best of ideas to file it as Fly Up My Cock, then, but it was intended to be helpful.  Midi made from notation in the Henry collection; the set came from Frank Thompson of Priestland, Bushmills, in 1937.

NOTES:

511)   BROUCHTY WA'S  [Child #258].  Sorcha posted an abc for this one back in February, which I think you may have missed:   Broughty Wa's.  Worth mentioning that the DT file title is spelled wrong!

338)   BILL PICKETT  and 2580)   OLD BILL PICKETT  are effectively duplicates.  The former credits a writer, the latter doesn't, but contains extensive background notes.  The two files need to be combined.  No idea about the tune...

1072)   FALSE SIR JOHN 2  This is Child's version C.  MMario sent a tunefile (Bronson, 4:83) to Joe back in April, saying that it was for   1071)  FALSE SIR JOHN.  This latter file states "tune & text from Bronson", which is only partly true; the text seems to have been cobbled together from bits and pieces (and the reference halfway through to a "bridge" seems pretty pointless), though the bulk of it is probably a modern anglicisation of parts of Child's C text.  Altogether rather unsatisfactory; there are so many genuine traditional versions of this song that it seems a shame to include modern, non-traditional collations instead.  Oh well; the tune is the right one for Child 4:C, anyway, and may well be the right one for the other file as well.  We can probably consider both dealt with.

Worth mentioning, perhaps, that there are mistakes of transcription in False Sir John (2), which look like the result of using an OCR program and not proof-reading the results.