My guess to the, "cylinder has never been turned," thing is that means there is no line on the cylinder from the cylinder stop lug dragging over it's surface. Just like you said.
For what is worth I do not think that Colts ever really drag on the cylinder. Only Remingtons do that. At least my Ruger does, and it is closer to a Remington clone than a Colt.
I also forgot to mention that the groove for the caps is probably NOT for a capper of some kind. The groove is just an aid for bare handed capping of the percussion cones. Fiddle around with your fingers and get the little cap into the groove, then run it slip it down to the cylinder and onto the cone.
One thing to also know about your new pistol. The Pietta .44 caliber 1851 Navy is just an 1860 Army with an octagon barrel, and thus made to look like the older '51 Navy .36 caliber. The giveaway to recognise that is the two step cylinder that has a larger diameter front half (it is also stepped down inside the chambers as well). The .36 Navy has a straight cylinder. Why is that important? You can get spare parts for your 1860 Army by either buying 1860 Army parts, or if that doesn't work you can use .44 caliber 1851 Navy as well since from the cylinder and on back from there they are the same gun.
The flip side of that is you see about buying the barrel and loading lever assembly of a Pietta .44 caliber 1851 Navy and mount it to your pistol and have your choice of designs you want to play with, and not pay full price for a Pietta Navy '51.