https://screenrant.com/schitts-creek-one-christmas-episode-reason/

Despite running for six seasons, Schitt's Creek only had one Christmas episode, which makes the show's already muddy timeline more confusing.

Schitt’s Creek’s Christmas Episode Secretly Paid Off 1 Missing Character Cameo & Alexis Tease After 3 Years (https://screenrant.com/schitts-creek-christmas-episode-stavros-cameo-only-appearance/)

"Merry Christmas, Johnny Rose" includes the only appearance of one often-referenced character during Schitt's Creek's Christmas flashback.

Johnny's Flashback In Schitt’s Creek’s Christmas Episode Created A Secret Reunion For 51-Year-Old Musical (https://screenrant.com/schitts-creek-christmas-episode-paul-shaffer-cameo-godspell-reunion/)

Johnny's flashback sequence in Schitt's Creek Christmas episode features a stealth reunion between Eugene Levy and another cast member.