When do Isabelle and Tom Nook change outfits?

[Cetoddle769]

I’m just curious about when exactly that change their clothing to match the season. Does anyone know of a specific date or month they do so? I’ve been searching online but nothing has come up.

 

[McRibbie]

iirc it's October 20th for the autumn/winter outfits, March 20th for the spring/summer ones?