I know I’m quibbling here since Toby has tweeted that all capitalizations were accepted, but for the sake of uniformity shouldn’t the page Undertale Complete OST be titled with UNDERTALE in full capital letters, in the manner of UNDERTALE Soundtrack?
The Complete OST is unfortunately not available on Toby’s Bandcamp (which would have otherwise provided an official answer, like it does in the case of the “Undertale Demo OST”), but Fangamer has it written “UNDERTALE” in full capitals, and the complete OST’s title being capitalized like the original one seems logical to me.
Undertale Complete OST is listed on Discogs with title-case Undertale. It’s also consistent with “Undertale Demo OST”.
I know, I had already checked for comparison, but the thing is I don’t consider Discogs a trustworthy source because even the “UNDERTALE soundtrack” (which is officially in full capitals since written as such on Toby’s Bandcamp) is simply written “Undertale Soundtrack” on their site