Polydor and Warner aren't related; this album's initial US release was on Tetragrammaton, which was licensed to Polydor in Canada. Warners subsequently got Purple's contract for the US, Canada and Japan when Tetragrammaton went bankrupt.
B1 track titles says...
Adeste Fideles on front cover
Adeste Fidelis on back cover and label
Misspellings are common. The correct title is "Adeste Fideles."