How to set End Mb in Nero CD-DVD speed

I’m testing all my DVD+RW media using Nero CD-DVD speed disc quality scan, because I think most of the discs are faulty.

However, one of them just gave me an error message “No Additional Sense Information”, but no POF failures and 93% quality.

I could be wrong, but have the distinct impression this error can signify a fault with the media, because if the media is full, then being unable to read any further because of unrecoverable read errors can cause the message to be displayed.

However, I have a feeling that in this case, the error has happened because the scan is trying to read past the end of the data recorded onto the disk (since it wasn’t full) - it was recorded using a Bush DVD recorder (like a sort of VCR).

If so

a) How can I determine the maximum Mb to put in the End box in the CD-DVD speed settings, or how can I avoid this error when the disc just isn’t full.

b) How can I determine if the error is due to the disc being full or if it is due to the disc being faulty?

Please forgive me if this is in the wrong forum, its about testing of media.