I have a lot of GOG games. I keep everything backed up on an external drive. I often reinstall from my harddrive instead of downloading again.

I bought a new laptop about 6 months ago. It has Windows 7, though I had been using Vista before. I'm noticing that not all games say they are compatible with Win7, but do they get updated? Am I better off to download the latest version before installing a game and then updating my backup, or are they the same file? Is there any way to know so I can avoid unnecessary downloads?

They do. As of now, the only way to tell are the checksums posted at the individual product pages of the wiki, but update notifications are a feature that should be coming soon.

The updates are released without any notes whatsoever, so we often have no idea what exactly was changed.

For any DosBox installer, I am sure it will work (for both 32- and 64-bit systems). The DosBox wiki says so: http://www.dosbox.com/wiki/DOSBox_and_Windows_Vista_and_Windows_7

For any other game, I would suspect it would depend entirely on the game in question. The installer would probably work regardless, but there might be a game in there that doesn't like some driver or other, or whatever.

Edit:
And, as mentioned above, the installers themselves occasionally change for various reasons, but I think it has more to do with the game version and/or included extras than the installer itself. I could be wrong about that, but I haven't had any trouble using older installers on my Win7 64-bit system.

The extras have no impact on the installer whatsoever.

Sometimes (I guess) a new patch for a game becomes available, causing the version number to change. Other times, GOG makes changes to the way they've "fixed" the game for modern OS's. Case in point: Heroes of Might and Magic 2. When it was first released, the music lay as redbook audio on a CD image which was mounted as a drive in DOSBox. Later they changed it (I don't know why) so that the music was in .OGG files. If nothing else, it makes the installer smaller, but of course the music is no longer lossless.

I meant that the file may change, not that it would behave differently. When I referred to 'installer' I meant the file itself, not just the installer portion (like referring to a self-extracting compressed file as just one file). I do see how what I wrote could be confusing though, so thanks for clearing it up.

Still not quite sure what you mean. Extras for a game are separate files, they are not wrapped in the installer file, and are not installed along with it. In fact, they have no connection with it whatsoever, other than the fact that you get access to both the game installer and the extras when you buy the game.

Whichever files the extras do come in will naturally change if the extras do.

Mainly was referring to the manual, readme files, or whatever else might be included along with the game in the installer. I am not talking about wallpapers and that sort of thing. I don't know why they would change, but if they did that would necessitate a change of the installer file as well. I was just trying to cover my bases with the response. Mainly it would be patches or otherwise changing the program to be installed that would lead to a new installer file.

But, it doesn't matter, because we are still saying the same thing about the installer itself.

While is has only happened once (afaik) they can change for the worse. RoA2 was changed to the inferior disk version some time after release.

Just to keep in mind before simply updating to the newest.

I thought the new gog.com downloader checked to see if there was an update to anything in its downloads folder? Or was that just a "coming in the future" thing?

Ideally, the site itself would have memory of when we last clicked the download links for a product and then let us know any products that have updated since its last download.

Update notification is marked as "in progress" in on wishlist.

This I did not know. Thanks for the tip. This will help let me know if I need to redownload things.

Thanks to you too Bazilisek. I almost gave your response the "solved" rating.

Just a little extra clarification if you want to check if older stuff have been updated (i.e. not downloaded with the new downloader), then when I said "...try to re-download something you already downloaded into the same folder..." it meant in the same folder it would have been downloaded if you used the new downloader.

The difference between the old downloader and the new one is that new one creates a folder per game while the old one was simply downloading all the files in its destination folder. (for example if you download "Age of Wonders" then the downloader will create a new folder called : "age_of_wonders" and put all the files in it.)

For the trick I mention earlier to work with games downloaded with the old downloader or through the browser you need to create a folder with the correct name (i.e. the name expected by the new downloader) and copy the game installer files in it.

Personally what I do is to download one of the bonus using the new downloader, this way it will create a folder with the correct name, then copy the game installer in it and finally try to re-download the game to have the downloader check if there is an update or not.

It can be time consuming if you want to check a lot of games but the good news is that you only need to do it once per game. (unless GoG decide to change the downloader's folders structures again)