What is a Written Word™?

_{This is in the spirit of the What is a Word/Phrase™ series started by JLee with a special brand of Phrase™ and Word™ puzzles.}

If a word conforms to a special rule, I call it a Written Word™.
Use the following examples below to find the rule.

And, if you want to analyze, here is a CSV version:

Written Words™,Not Written Words™
GOOD,BAD
JANUARY,DECEMBER
HAPPY,SAD
JOKER,CLOWN
GRAVEYARD,GRAVE
HYPER,SUPER
EIGHT,SEVEN
EGYPT,ISRAEL
POLICEMAN,FIREMAN
QUINTET,TRIO