So now realizing what should be happening, & looking to see that it does happen, I can say it is not happening.
flashgot.exe in my main SeaMonkey 1.1.17 Profile has remained the same old, flashgot.exe of 04/30/2009 (which looks to put it between 1.1.8.6 & 1.1.8.7 - perhaps).
(Now I'll surmise that once a particular version has been installed into
any Profile, that subsequent installs of the same will no longer update the flashgot.exe file in other Profiles. So if I revert back to some older version, then back to current ...)
Nope. Made no difference. Same old flashgot.exe.
Looks like the only way is to manually delete flashgot.exe.
And upon restarting the browser - without reinstalling FlashGot, it was replaced with a flashgot.exe
dated 08/12/2009 (& current time).
Which it pulled from where? ... Has to be from Global / chrome / flashgot.jar - which is an (yet) OLDER version I put in (03/13/2009), so even though flashgot.exe is "dated" current it again is still actually going to be old.
Yes, this is the case. It is the flashgot.exe from my flashgot-1.1.8.xpi.
This is confusing.
(Wasn't there a time where flashgot.exe was deleted on browser close, & was put back in on re-open?)
So Luddites of the world, paying attention

.
Could flashgot.exe have an internal version number so that if you checked Properties it would display, alleviating confusion from looking at a currently dated file that is actually a dated file?
Could flashgot.exe be installed Globally rather then in the Profile.
(This would, I believe, only be a SeaMonkey 1.1.x issue. Not affecting SeaMonkey 2 or FF2 & later.)
(Is it worth even dealing with other then just to know that the problem exists?)
So, install latest. Shutdown browser. Manually delete all (SeaMonkey 1.1.x) instances of flashgot.exe. Restart browser.
Then as each Profile is loaded, it will pull from the Global .jar file, that version of flashgot.exe into the Profile.