About the manuals, you should send a chat message to Linko90 about this, he should be able to direct you to the right team to help GOG add manuals where they are missing.
Thanks in advance for this, by helping on this front all GOG users are going to benefit from it ;)

Regarding manuals, would you consider scanning and uploading them to replacementdocs if you haven't already?

Be careful about sending them to GOG. I maintain a list of games with missing manuals and when contacted GOG regarding adding the missing ones to game cards my support ticket was ignored. After prodding them later they replied, but just gave a generic "sorry can't do it". I don't think the guy even bothered to check, since some of the missing manuals are available in the game's directory, so there is aboslutely no reason, legal or techincal, not to add it as an extra goodie too.

There is also this thread
https://www.gog.com/forum/jagged_alliance_series/jagged_alliance_1_strategy_guide/post30
Where a guy bought a game guide for Jagged Alliance, got the green light for sending it (in 2015) so that it will be included with the game, sent it and... nothing. I can understand there might be more legal reasons with this, but in that case they should at least tell him so "Sorry, but after all we can't include it." If you follow the thread, you'll see that despite of reminders, almost 4 years later this is still in limbo and no one knows why.

So if you want to send any discs or manuals to GOG... be careful.

EDIT: Oh, a necrobomb.

My biggest issues right now would be 1) not knowing what is "missing" (I have a lot of stuff, but GOG has been pretty good with most older games having their manuals and extras). 2) gaining access to my stuff, as a lot is close by but a lot is also packed away in storage. :(

I would be happy to donate them to Replacementdocs too, though right now they are in a pretty poor way (requiring workarounds to download from and AFAIK no way to upload to), and it's scary to think they might up and lose *everything* overnight considering what a vital resource they are to retro and modern gamers alike.

re: GOG, thanks for the heads up. That said, I would be definitely scanning or archiving any discs or manuals or guides myself rather than sending them overseas. I just wouldn't trust them not to get lost along the line, no matter how careful GOG themselves were. I'd honestly rather buy a new scanned best suited to the job at my own expense than risk sending rare collectables for someone else to do it... though this is why I have so much that is unscanned/unripped, due to time constraints and knowledge of how best to preserve it.

I hate to think that some of these cool pieces of documentation may be lost forever, and if GOG doesn't want them, that's fine I am happy to post them elsewhere for those who own the games to download. For example (not GOG-related as such), I scoured the net the other day to find the manuals for the old Amstrad PC1512 and PC5286 game bundles I used to own, and was surprised that it seems there are no scans anywhere of those. I still own the manuals myself (just wanted them digitally for ease of access) and would be happy to scan them so they could be preserved, but they're pretty thick tombs, especially as they're in multiple languages.

Disk images/ISOs are trickier, especially if they are still being sold in some form (i.e. GOG), hence why I was thinking it would be best if GOG provided such things as "goodies", and my thoughts to help. As with my previous post example, GOG downloads work great (mostly) with new machines, but if I want to run many of these on an old DOS PC, due to many being pre-patched or having their old installers removed, I'm back to either abandonware sites or buying second-hand copies at inflated scalper prices! Not to mention, the historical preservation factor of many old releases containing fascinating stuff (even inside their installers, in some cases) that was never included in future (or GOG) versions.

Personal experience note: I do know that Prisoner of Ice got the "newspaper" extra added because myself and another user persisted asking about it, and the latter provided the scans to GOG.

Would you rather me start a whole new thread? I searched before doing so, assuming others had likely wanted ISOs at some point too, and this thread seemed relevant so I added to it instead.

Complaints of "TL:DR" and "don't necro old threads!" are pet peeves of mine, and a sign of why stuff like Twitter is sadly replacing forums and real discussion, IMO. Just my two cents.