I can’t speak for the sending of existing code you’ve already done, because I’ve never done that. I have done interviews where the initial stages were vague, a

I can’t speak for the sending of existing code you’ve already done, because I’ve never done that. I have done interviews where the initial stages were vague, and they couldn’t go into any more detail until you had signed the NDA. IMO, that’s normal for interviewing for a position at a company or a group inside of a company that has not yet launched their product, or is otherwise doing sensitive stuff.