This is a good point, BUT nobody has showed evidence the reason for the spare cylinder was, and only was, a "quick reload".
The problem with this is "damaged" from what? How? So you don't get the revolver repaired OR it was so badly damaged that it cannot be BUT the cylinder survived?
Again, this simply shows that as far as the army is concerned, the government wasn't buying and issuing spare cylinders. So you're probably not swapping cylinders if you are a private in the cavalry.
The first article mentions that when the conversion cylinders started to appear, some revolvers were sold with the conversion, BUT still came with a cap-n-ball cylinder. This is in case the owner can't find cartridges, and has to switch back for a time. THIS might be the key, but not quite the reason....
So the cylinders are NOT for a "quick reload" but we can find scenarios where they could be faster than the conventional way of reloading. WE however miss a couple points.
ARE they for reloading in combat, OR CONSIDER..., was the owner of such a cylinder a little wary of the durability of the cylinder in his revolver? There were a LOT of fakes made of Colt's open top, especially the .44 versions. Steel quality in these might vary a lot, and they were often tough for a person not well versed to detect. EVEN IF the person could tell the revolver was not really a "Colt", did they have the option to buy a different revolver, or was it the default option for them?
Which brings up the question, Had these still existing examples of spare cylinders of which many are still loaded, been carried by folks who had seen or actually experienced a chamber failure in the past? Not necessarily a catastrophic failure where they were injured and the whole handgun ruined, but one where the cylinder cracked and deformed a bit? Did they carry that loaded second cylinder because although slow, they thought they might have a chamber failure and would need to replace that cylinder ASAP?
AND the fact that when a person got a conversion cylinder, they kept their original cylinder, PLUS the revolvers sold with a pre-fitted conversion cylinder would come with the previous cap-n-ball cylinder. Folks assuming that was for situations where cartridges were scarce. Really? OR was it also because the buyers of the new tech of the conversion cylinder were not fully confident the cylinders wouldn't fail? HOW do we know that all of those "spare" cylinders, especially those found loaded, were not mostly carried by folks using conversion cylinder revolvers, and those cap-n-ball cylinders were the extras, and loaded "just in case"?
So perhaps it WAS commonly done, when one had a conversion cylinder, and those conversions were "all the rage" for about a decade.
LD