I think he figured out that Castor Oil -moves- lymph fluid in a noticeable way; (especially noticeable if a person is congested)
For example, my personal experience has been: being toxic and congested at a point in my life- using the protocol of castor oil packs over the liver-thymus-spleen, I began with the thymus.
A couple days after this first thymus pack, I became extremely fatigued, and broke out with several boils on the torso.
3 days later, had a cleansing bowel movement, and a all was better.
This indicated to me that the liver ( comprised of large percentage of lymph) was congested, and the castor oil "moved" the toxins in my lymph system too quickly for the liver to detoxify, so they backed up and came out of the skin; all the while poisoning other parts of the system and making me sick.
I think 80% of what is wrong with people is toxic congestion, and when we get detoxed, the body uses it's own intelligence to correct the ills.
This can be seen as a miracle; I know that it did to me.

So he prescribed CO packs often, and often got results.