John,
The last time I had a Jeffery daybooks search done was now about 3 years ago.
At that time the existing records (only the old daybooks exist) were located in the Friedkin private collection near Houston, Texas.
The requests for research were done thru an executive assistant at “The Friedkin Group” and were done only about twice annually.

I have no idea if the records search process is still the same; last I heard in 2022 there was some talk of the Jeffery records being transferred or sold to an entity that would offer more availability for records research?
It may still be possible to get updated info by contacting the Friedkin Group, Houston, Texas and asking for assistance.
- Mike