In article , Sandman
wrote:

The Olympus E-M1 II has the lowest noise at ISO 64 (at the cost of a bit
less dynamic range) but the highest dynamic range at ISO 200. So what
would be the native or base ISO of the sensor?
How would that be defined?

Unless the camera maker doesn't specify this specifically, there is no way
to know when the sensor output is boosted or not.

there is.