A bit ago I had a question and some said to me here, that the Answer to my question would depend...
Depend on whether or not I am/was play through "Galaxy".

I believe their exact words were "If you're 'using' Galaxy..."

I'm curious about whether that means Loading my browser, signing in at the www site and playing that way...?
Or using the desktop Installation for GoG game management "which you don't need" to use anyway being that it's all DRM free.

The 'context' of my original question was with regard to the installation of extra content and how you know if it's installed or not.

Okay then... what does it mean to be "using Galaxy"?

>.>

GOG Galaxy is GOG's client - the program you use to download and run your games, keep track of your play time, get achievements, etc.

Edit: And to clarify even more, you don't have to use Galaxy, you can download game installers through a webbrowser, and run them without the client.

Galaxy might tell you if extras are installed or not, don't know don't use it.

Depending on the type of extra, the game itself might tell you via menu options once started. Other than that, you can check the individual forum for each game and even ask questions there if necessary, to find out what the go is.

You could also check the install folder for file or folder names that might give you a clue, or the installer files (packages) using something like Inno Extract.

And if all else fails, ask the developer or consult some website.