I believe that the Kokarden could go either way. Here are a few tips that I use when trying to determine originality. First, the Kokarden were stamped instead of cast, so if they look cast (bubbles, subdued areas, etc) they are not original to that helmet. Anything older than 1860 bears closer scrutiny. Second, since the Kokarden were stamped the flare on the inside hole goes outward toward the chinstrap fitting. The first reverse photo you have looks good to me. The second reverse photo shows that the flare has been turned back inward. That inward turn is usually a sign to me that it is a reproduction. Third, take a look at the rust. You can often tell old rust from new (buried in the backyard) rust. I can't really explain this, but maybe you can understand what I mean. Last, you should weigh the Kokarden. I have found, 100% of the time with new repops, that a reproduction Kokarde weighs almost twice as much as an original, even if it is stamped. All that being said, these Kokarden are very convincing.
As for the chinstrap, it too could go either way. The reverse side should not be dyed; however, many of these turned dark grey, dark brown, or almost black with use. I have several like this. Sweat screws up leather something fierce. Also, some collectors in the past, in trying to "save" the chinstrap coated them in leather dye, black shoe polish, etc. It may be one of those, original but messed with. The fittings on the chinstrap should be roughly 1mm thick (see here:
https://pickelhauben.net/m91-chinstraps-side-posts/ ). If they are thinner than that you should be skeptical. Glue on a chinstrap, especially at the buckle ends, is a dead give-away that something is wrong. This does not include glue that some former collector has used to try to make a cheap repair, though that is not a pleasing aspect either.
It's a beautiful helmet and I would be proud to own it.
Congratulations!
John
It´s sometimes very difficult to see the difference, it also applies to me.