DVD Burn interrupted - is the blank a coaster (1 Viewer)

So I'm making Video DVDs on my 'puter (using CyberLink Power2Go software) using (cheap) DVD-R blanks. Most burns go ok but a few have been "interrupted" (even tho i burn at conservative 4x speed and (suposedly) have buffer under-run protection). In some case at about 10%, sometimes 50% through. As I said the blanks are cheap and I know DVD-Rs cannot be erased/reformatted per-se, but there's clearly alot of unrecorded space on them so I'm wondering if there any thing I can do (any software that will) delete or 'cover up' the stuff that was recorded and recover the disc as a usable blank albeit with less than the normal capacity. OR, perhaps 'clean up' the stuff that was recorded as a usable (viewable) track and (perhaps) I can use the rest of the disc to add stuff in another session. Or are these blanks only good for drink coasters, target practice, etc. Many thanks.

Yep, they are coasters if they don't burn all the way through to a TOC