All DVD writers and CD writers will burn an "inner circle". That is usually one way to determine how much space you have used on that disc without popping it into your drive.
Hm... how long have you had your DVD writer, and estimate how many DVDs have you probably burned since you've had it. DVD writers will go bad after too many uses, I've gone through 3 or 4 CD writers since 1999, and I can vouch that burning CDs is like driving on tires. They serve their purpose, but every time you use them, the sooner they will need to be replaced.
I have a NEC DVD RW ND-3520AW, and it seems to be working fine for me without the required firmware updates.
NEC is known to release firmware updates religiously for our DVD burners. You might want to check to see if yours might need to be updated. Here's a link to the last release of the firmware.
http://forum.rpc1.org/dl_firmware.php?download_id=1904