I assume everyone involved in constructing the Control
Code for the Tuner
Dongles started out by recording the I2C stream on the Dongle coming from
the Original Dongle Software that comes with the Dongle for watching TV and
FM Radio.
As far as the e4k is concerned: We're currently using the OsmoSDR driver
which was written by people who have access to the e4k datasheet, this
driver predates rtlsdr by quite a bit, and I'd dare to say that it is
unwise to modify constants used by it unless your datasheet disagrees
with ours.
Unfortunately there is very little known about the other tuners, so
their code is mostly just modified v4l code.