gud2ya
When a traceability exercise isperformed, only the relevant materials are inspected and +/- 100% would be expected
If cartons need liners, and employees damage and throw out 20/day or 100/week or 400/month or 4800/year and you aren't aware of that your tracability on packaging would be out, but you don't know where they've gone
Dry ingredients could get spilled and no one weighed the spillage so it looks like you've used it but you actually haven't
The entire idea of the exercise is to improve! And you cannot do that if you don't know where the issues are and you can't do that until you perform the exercise
Exposure to air makes it heavier? I would hope any material that could do that (let's say flour for the sake of argument) is properly stored so that doesn't occur