A Coldport Christmas puzzle

Detective Inspector Playfair, an energetically boisterous policeman who often complained about Endeavour Morse having his own TV show, was sat on a bench at the side of Coldport's newly laid town square (Tile-laying for beginners ) holding a lacquered programme in one hand and a steaming-hot cup of coffe in the other. Miss Flava, who had worked with him for years, was patiently awaiting the outcome of his deductive methods.

"Coldport's Choral Ecdysiasts," said Playfair, "know more than they're letting on about the theft of an artefact from our museum. We have a man on the inside and he's sent us a message via the programme for the concert tonight. Only his handler is off sick, and I have don't have time for him to recover."

Miss Flava looked at the programme. Inside the first page was a ticket bearing the words

Admit three to room one at quarter past six pm on December nineteenth.

After that was the concert listing:

• GQ PKF DOFOH GKBXGQYKD
• QN OLHF TTAP C GKSQKHKP ACBOC
• DDYB OGKE QKB XHPUDO'D VGVAY

and finally there was a "fun page for children" where they could turn their names, letter by letter, into Christmas phrases.

"I'm a fan of Acboc," said Miss Flava, "but I find Vgvay a bit... ecumenical. And--"

"Ignore the typo in Hanukkah," said Playfair, "it's not part of the puzzle. I know that there's something common to items in the concert listing and it will lead to the message we're after. I just haven't worked out what it is yet...."

Using the clues provided, find a three-word message to D.I. Playfair.

[An ideal solution will lay out the clues and how they lead to the solution: just the three-word message is not enough.]

• Is the three-word message meant to make sense? Because I've found what's common to the items in the concert listing and there's an obvious way to get three words out of it, but those three words don't really seem like the sort of thing that would help the D.I. to find out anything about the theft... Dec 11 '19 at 17:31
• (The thing-in-common has at least one other fairly plausible interpretation but that doesn't seem to lead anywhere useful either.) Dec 11 '19 at 17:38

First of all, the ticket says

(extracting just the numbers) 3 1 18 15 12 19, which by A1Z26 turns into CAROLS.

Now

using that as the keyword to construct a Playfair square, and decrypting the gibberish with that, we get:
IN THE BLEAK MIDWINTER
IT CAME UPON A MIDNIGHT CLEAR
SEXE AMID THE WINTER'S XSNOW

(I remark pedantically that "a" should really be "the").

Now,

what's common to these carol names? MID, of course: midwinter, midnight, amid.

And

that translates via the children's code to TRUST EMMANUEL SHEPHERD. Perhaps that's the name of some person relevant to the case.

Incidentally, a concert of choral ecdysiasts sounds pretty entertaining.

• You are right about the three word message regarding E.S. and I'm sorry you found it disappointing. I am working on a second part to this which will hopefully make this message more satisfying, but obviously puzzles should be posted one at a time. I'm a bit wary of putting too much flavour text in, but maybe in this case I should have set up a bit more that tied it all together more strongly? And... thank-you for noticing the ecdysiasts ;-)
– user40528
Dec 11 '19 at 18:13
• By the way, I couldn't find any agreement in various lyric sources for the place where we disagree on "a" vs "the". I'm quite happy to believe you're right :)
– user40528
Dec 11 '19 at 18:14
• The oldest things I can find say "the" rather than "a", and the relevant Wikipedia article specifically says "the but sometimes rendered as a" -- but I could be wrong. Dec 11 '19 at 18:39
• I think putting in enough flavour text to make this particular set of words obviously relevant might have made the puzzle too easy. (Or at least made it apparent what the final answer was going to have to be.) Dec 11 '19 at 18:39
• (Now that the answer has been confirmed, I've removed the bits of my answer where I wondered whether it was right or not.) Dec 11 '19 at 18:41