I had a multi-session DVD-RW and the last track I wrote seemed to burn fine and the disc closed without an error, then later when I put the disc back in it reads as a blank disc 
Under windows explorer and every burning program I’ve tried it shows as blank, are there any data recovery programs that can read a DVD-RW with a missing or corrupted TOC?
Try it in a different computer. I had this same issue - where Windows gets it in its head that the disc is blank, and refuses to believe otherwise, even if it’s false.
Failing that, I had success with this: http://www.jufsoft.com/badcopy/