How do I know when an update is available?
You would get a notification from the Live Update, which will prompt to you run it, in order to get updates.
My last installer was version 2.2.0.0 and I DL by chance again and now the version is 2.2.0.4 with some updates (thank you).
If you noticed new features, it can only mean you must have had a Live Update notification and ignored it. If you ignore a Live Update notification, it won't notify again, until the *next* update, unless you explicitly select the "Check Live Update" menu option from the "Couatl Live Update" menu under "Addons".
In that case, the Live update would give you another chance to read the release notes and install the update, with no need to download the new installer.
In the support forum I find the topic "GSX 1.9.9.11 - Major update " but nothing about this (2.2.0.4) update.
That's because we don't need a forum message anymore, since we have a notification system inside the sim. Not all users go to the forum, but surely everyone use the sim.