Does it matter how a date is stored for localization? (time not stored)

I store dates as strings in the following format:

YYYY,MM,DD // "1969,12,31"

I intend to format that string depending on the user's locale on the frontend. Does it matter what format it's stored in? I imagine it doesn't matter, as long as I know how to parse my string on the frontend. If it matters, I don't care about the time, just the date.