First, be sure you don't confuse the message about an Major Update, that requires to exit and download and install the Stand-Alone Addon Manager, and a Minor update, which require only to have the program launching the updater, which can run while FSX is running.
We only had ONE Major update notification, the day KMEM was released, and *several* Minor updates after that.
I've just checked now (using the "Check for Updates" option), and I can see the release notes dating June 2nd 2016. No idea why it shows the outdated release note file on your system, maybe your browser cache settings are playing a trick on you.