What is the difference in meaning between these two sentences?
I didn’t know you weren’t in.
I didn’t know you wouldn’t be in.
I didn’t know you weren’t in. This means that the speaker thought someone was “in” when they weren’t.
I didn’t know you wouldn’t be in. This means the speaker predicted that someone would be in, but they wouldn’t be.
The difference is in when the speaker thought they would be in: while they were thinking it, or later on.