Can Nimbus experiments/rollouts target specific beta releases, i.e. can I express "roll this out to everyone on 104b6 and later"?
If you are a mobile engineer, see steps here for how to add a version.
The version requested will get added as an option to the Minimum Version and Maximum Version drop down menues. It is a minor and quick change. By default Experimenter (Nimbus) only exposes the whole valued versions, until requested.