Is it "Noel"...
...as most spell it these days?
From Dell's Santa Claus Funnies #1 (1942), illustrator unknown
Or is it...
..."Nowell", as seen in Dell's Four Color #91 (1945)?
Illustrated by Arthur E Jameson.
"Nowell" is the English (British) spelling...and the hymn is of British origin.
"Noel" is the French (and other Old Latin-based languages') spelling.
Presumably it became the standard when the hymn was used in hymnals (which used Old Latin verses for many songs, though I've never heard an Old Latin version of "First Nowell") in the 18th Century.