According to what Disney has published,
DAS for AP holders is authorized for up to 60 days. As other posters mentioned, it is on your profile, which a linked Magicband can access. Nothing from your profile is actually stored on the Magicband.
If it's been longer or you don't have an AP, you would need to get it re-authorized before you try to use it. That doesn't have to be your first day.