1225 is for the Holidays as a whole, not just Dess!

For instance, Noelle’s blog in the Spamton Sweepstakes is Holidaygirl1225. Yes, the blog is Noelle’s. So this is a case of 1225 linking to Noelle, instead of Dess.

Sure, the code in Dess’ guitar is most certainly 1225. But 1225 in Tenna’s world can easily be associated with Carol. Parental controls would be set up by Carol. And Toriel. Now, the secret room you get from 1225 POINTS, okay, probably Dess-related (only because the theme song of the area you find it in is “findher, and Noelle is definitely not related to the black shard). But not every 1225 reference is automatically tied to Dess. The other Holidays also are tied to that number. So it’s best to think of 1225 as related to the Holiday family as a whole. Not specifically Dess. So we shouldn’t just jump to Dess every time you see that number.

Also, “Lost Girl” was referred to by Toby as Noelle’s theme, but also playing when she’s absent. So “Lost Girl”/findher isn’t purely a Dess motif either. Noelle and Dess are both feasible subjects for something with that motif.

I think we’re all being a bit too quick to link everything to Dess. Yes, Dess is important, but the current state of things here in the fandom seems like the Deltarune equivalent of 2015/2016 when we thought literally everything weird in Undertale was Gaster.

However, findher.mp3 IS related to Dess, as this is Dess' guitar.
Your point about it being related to the holidays as a whole is mostly correct.

In the Spamton Sweepstakes, yes, that iteration of findher is Dess.

But hearing the leitmotif elsewhere doesn’t automatically mean Dess is involved. (For instance, if it turned out that the same melody was indeed found in Black Knife [something I doubt the accuracy of, and it seems so does the wiki since it’s not there], that would not imply that Dess is the Knight. Or… even linked to the Knight, for that matter.) Because that same melody also applies to Noelle, implying it’s a melody for the Holidays as a whole.

Also, even then, Lost Girl is just a random leitmotif, used anywhere Toby wants, really, but it has prominence in the Holiday related music. :/