Tracker firmware vs SDK version

[Guy_]

If a tracker firmware does not get updated to the latest level does the device not see clocks/apps developed with a more recent SDK level?

In fact can the device only see older versions of clocks/apps? 

If true how are older versions of clocks/apps stored on the site?

Example. If a clock was created with SDK 4.0 and then later published with 4.1 can users still see the clock in the gallery but only the older version and not be able to upgrade to the latest version?

[JonFitbit]

Each build you upload is associated with your clock/app. The gallery ensures the most recent compatible version is installed on your device. 

If your device firmware is Fitbit OS 2.0, then you'd only be able to install builds which were SDK 1.0 or 2.0.

If your device firmware is Fitbit OS 4.2, then you'd be able to install anything built with SDK 4.2 and lower. 

[Guy_]

Thanks for your clear feedback, that is what I understood.

But what does a tracker with an old OS 2.0 firmware see in the gallery, is more the question?

Does it see the latest instance of the clock/app built with OS 4.2 but can only install older versions made with SDK 2.0, or 1.0 for instance, if there were any?

In other words do older clock/app versions persist when newer versions are published to cater for such cases?

In the case where there were never any older versions [ever made] will the user be unable to see the clock/app in the gallery at all? Or will he see it but be unable to select it for installation?