In general they are either desktop only like ControlsExDesktop or for both, in that a device specific library like ControlsExDevice will in fact include a desktop dummy of limited functionality like ControlsExDevice Dummy to allow desktop development. Therefore in practice I think that you can regard a library archive as an individual entity and not worry about its intended target.
No matter what I do with the contents I keep any downloaded archives (mainly dzts) in a single archive folder and extract them any time I want to reference them. So in my case just scanning that folder will tell whether I have downloaded the latest version.
I seem to remember that Cableguy implied in a previous post that Erel doesn't want any automatic downloads happening.
I thought the discussion was that he didn't want automatic updating in the background (kind of a continuous check & update, or something scheduled like Windows update)
However, automatic updates would be a user configuration. By default, the program would not update automatically. And if it's not something that anyone wants, I'm not going to spend any time coding for it.
I ask about platform versions because a future release might run from the mobile device. It wouldn't make sense to check and download something that is specific to the PC.