My apologies if you already know this, but it came as a surprise to me.

If you create a disc from several projects, using the project files rather than rendered video files, then decide to modify one of the projects; when you create the disc you still get the old version unless you delete and re-select the modified project.

So if you need to modify the project on a disc, you need to go to the 'Disc' tab then select the 'pencil' option for that project, rather than simply modifying the original edit.

Gary.