In my TI-83 Plus manual (which I still have, despite no longer having the calculator), there is a screenshot showing TI-83 Plus OS 1.00, but the oldest OS I ever saw on a real calculator was 1.03.
I wonder if anyone ever managed to find it, if it exists at all?
(https://media.discordapp.net/attachments/491856847083405345/689532598577266855/unknown.png?width=1046&height=677)
https://media.discordapp.net/attachments/491856847083405345/689532598577266855/unknown.png?width=1046&height=677