Bumpety bump bump!
I performed some tests (on crappy DVD+R media) to see exactly how much data I could put on a DVD+R and still have room for a minimal (5 mm) DiscT@2 label.
On a normal DVD+R there is room for 3589 MiB data and a label, but not 3590 MiB.
The tested DVD+R media is 2,295,104 sectors of 2048 bytes which is 4,482.625 MiB.
This means that 893.625 MiB free space is sufficient, but 892.625 is not sufficient.
I also burned a DVD+R leaving exactly 893 MiB free space, and there was not room for a DiscT@2 label.
3589.000 MiB on DVD+R leaves 893.625 MiB free space which is enough.
3589.375 MiB on DVD+R leaves 893.000 MiB free space which is NOT enough.
MiB = 1024 * 1024 bytes
EDIT: A little more free space is needed on DVD-R media is seems (893.625 MiB free is not sufficient), so I'll make a few more tests on DVD-R media.