Fact that both of you are referring to "Dismiss" option in your menu, leads me to I believe there must be some kind of misunderstanding to what the Live update is telling you:
The "Dismiss" menu option is ONLY present if you see THIS menu:
"The latest Couatl™ Live Update is already installed"
1 - Re-install the latest update (doesn't require quitting FSX)"
2 - Read the latest release notes
3 - Dismiss
This is what you are supposed to see if you do a manual "Check for Live Update" from the Couatl menu, and you HAVE the most current update. There IS a "Dismiss" option, which simply means "close this menu", nothing more.
The above menu does NOT come out automatically, it will only come if you check for an update when you have everything updated.
Instead, when there's a new update detected, the Live update will be different:
"A Couatl™ Live Update is available"
1 - Download and install the update (doesn't require quitting FSX)
2 - Read list of changes in this update
3 - Ignore this update
See ? There's NO "Dismiss" option, but there's an "Ignore" instead. The ignore option means "I'm not interested in this update, don't notify me automatically anymore, until the NEXT update will be released"
When the update is major, that requires installing the Addon Manager, the only different option is the 1, which will say an "Addon Manager update" instead of a "Couatl Live Update" is available, and you'll have to quit from FSX to apply, but still the 3rd option will say "Ignore" NOT "Dismiss".
There are no menus anywhere in GSX with a "Dismiss" option that pops out automatically so, the only way you might have seen a "Dismiss" option, is if you manually checked for an update with the most current version available already installed, so it's exactly how it's supposed to be.
So, please, try to describe more precisely what you are doing and what you are seeing because, right now I still don't understand what the problem is. You have the most current, you check for an update, it says is already installed, so what's the problem ?
We might need to investigate if, instead, you were getting the "A Couatl™ Live Update is available" too often but, since you are keep referring to the "Dismiss" option, which doesn't exist in the "Live Update available" menu, that doesn't seem the case.