Can you provide more information on what books you've already checked? Makes it easier for others to help.
I also like to add that someone will know that Nibbana happened, for lack of better way putting it. Things change permanently on a deep level. That change doesn't happen with bhavanga. So, there are clear differences that can be known. Not just change, the content of the moments before and after are also different.
So, if someone would ask me whether (s)he 'was in Nibbana' I would point to the defilements. Are they still there? If yes, then more work has to be done. Nibbana itself is, in that sense, not that interesting. Only the presence of the hindrances is. With that approach there is no need for a book. Something to consider.