A clue might come from when the blessing "God Rest Ye Merry" was current? (And where and for how long?) Perhaps it still is used, but it's "unrecognized" in my parts.

I'm told that, spelled "correctly," the title is

"God Rest Ye Merry, Gentlemen"

and NOT

"God Rest Ye, Merry Gentlemen"

(as most commonly sung in the US at least.)

John