I've noticed that only newer purchased games give notifications for updates. In at least one instance a game purchased in 2008/2009 was update with no notification ( Divine Divinity).
My initial Purchased Version of Divine Divinity was Build 1.04a but i noticed from the forums that a newer Build was available so I needed to re-download it.

Is it possible to indicate installer versions on the Game Panel in My Account or to Sticky an installed version at the top of each specific game thread?

Actually, all game updates create such notifications, but this feature has been live for just a few months. If it updated any time before that, you'd get no notification whatsoever.

For (hopefully) up-to-date installer version numbers, check the GOG user wiki.

Lately the version numbers are part of the filename, so it would be fine to see the filenames also in your account and change the missing installers to the new filename scheme.

Edit: Ah, some games already show up with version numbers on the account page, so it's just the question how complicated it would be to make the same also for older releases.

I checked Versions on the GOG Wiki. There's quite a few installers I need to update:
Arx Fatalis, Fallout 1, Fallout 2, HOMM3, Ishtar Trilogy, Lords of Magic, Might & Magic 6 Compendium, Planetscape Torment, Settlers 2, Simon the Sorcerer 1 & 2, The Incredible Machines.

I only checked game bought between 2008 and early 2010.

I'll need to verify others but it appears Dosbox and ScummVM engines are out of date in most installers.