Jaycee,

You appreciate they don't dye the hair they need, as they need it, one system at a time?
They are producing hundreds / thousands of systems and therefore dye the hair in vats/batches.

That way they have the hair to blend & mix.

Your system, for example had 2 different colours in it.
How would they then dye it 2 different colours once its been made?

I'm not sure, but as the hair starts out black from the donors, it maybe isn't processed as much as when it is dyed other lighter colours.
This may be why its harder/impossible to bleach the knots.