Most of the patent reference data on this site was build from bulk downloads the uspto
made available. datamp.org graciously provided additional data as shown below.
(being a developer of datamp.org has its benefits!)
Students of mathematics may notice an apparent discrepancy. The counts shown are unique patents.
The data from datamp.org contained multiple patentees when applicable so there can be multiple references to the same patent. Ex. Patent 1,041,451 was issued to George O. Leopold and Thomas J. Fegley.
It was added to the reference table here twice. Once as "Leopold et al." and once
as "Fegley et al.". A user's search here could find either. The uspto data generally
only ed al.'s the first patentee listed (they'd only have "Fegley et al." as Thomas is listed first on the example patent).