Yeah, there's no reason to bring it up if this is a different book. Eight years is a long time and it won't matter at all that you didn't say anything about it. I know I wouldn't bother with that complication (of explanation, not problem; this isn't any kind of mark against you or your record - lots of people have manuscripts agented that don't sell and go on to plenty of success!)

You're a new you, as you say. : )

Best of luck!