Other items to consider relative to the "swish it in a jar" test:
1. The motion in the holding tanks is nothing like the motion in a jar being actively swished around.
2. The temperature is different.
3. The composition of the liquid in which the TP is being swished around in a jar is different from your holding tank contents.
These things, and others, will affect the breakdown results.
In other words, all the test is really showing you is how TP will break down when swirled around in a water filled jar. It does not replicate what happens in a holding tank.