Shmacky-McNuts: Gog not making every game they currate archival, as in, have many previous versions should be obvious to why. It would require to much money for so many versions to distribute to so many customers.
Knowing the gog crowd. There are many here that would download every archive in full. As crazy as that may seem. Im certain there are many that would. That opens up a huge amount of problems, when many games can be as large as 100GB.
Imagine even 500 customers grabbing 6TB of extra data for the "just in case" way of thinking. Its not a big deal when 20 people do it. But gog is a business. Not a library. My point is, each person must do this for personal use. It makes sense for a public distributor. But gog is a business that gains nothing by allowing previous version to be had.
Yes and No.
It would require knowing how many would and how many wouldn't, and I bet that most wouldn't bother. Hell, a lot don't even bother downloading the Offline Installer files.
A select few would do it, but by my estimation that would be quite a small group, and they won't all be doing it at the same time for the same game, except in rare circumstances, like a free game perhaps.
You also have to consider the cost of drives to accommodate such extra versions, so even if many would ideally like to download them, they cannot afford to, or might just do it for games that mean the most to them.
And it is very likely that games with lots of huge files will be bypassed in many instances.
So in reality, accessing such an archive of older versions, would mostly be done by folk that need an older version due to some issue that might require a rollback. So in other words they do it when needed, not before.
GOG could easily make archives of older versions unavailable during big sales, maybe even reduce their access to off-peak.