May I have the benefit of your collective wisdom on the importance (or otherwise) of combustion ending before the bullet exits the muzzle?

I use Quickload to predict the internal ballistics before working up a load, and I find that if I use the actual dimensions of my case and bullet instead of the figures in the database it agrees closely with reality.

For example, QL predicts an MV of 2578fps for 45gn N550 with 175gn Berger LRBT and I measured an average of 2555fps. It also says that only 96% of the powder is burnt before the the bullet exits the muzzle (the barrel is 26").

QL also predicts that I will get a very similar MV for 42gn of N540 for a slightly higher chamber pressure but with 100% of the powder burnt.

Given that my N550 load is giving me very good results at 1,000 yards, does it matter that not all the powder is burnt?