I'm not a lawyer, and the rules get messy - I'd need to do at least a few hours of research to answer you with any confidence. The type of stuff you're talking

I'm not a lawyer, and the rules get messy - I'd need to do at least a few hours of research to answer you with any confidence. The type of stuff you're talking about is not addressed by the code itself, it's tangled up in case law, which is the reason that lawyers go to school forever. Personally, I would write that 'previous work' as a library, open-source it, and then use the library at the company later. That's clearly safe.