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Accessories are designed for install by the dealer, and the dealer would be privy to the latest install procedures. (There was a design change early on, in fact, I believe it was from early non-production to actual production vehicles.) The brush guard kits were made long before, and later sets should have the accurate install procedures, which are available online for GM dealers. I believe, the change to the D-rings was done for safety.
The marks are for quality control, and could be on a vehicle run this week. It is a periodic control process. Can you notice them when not under the vehicle?
Yes, the shield requires removal, all of two minutes with the correct socket. This is not unheard of on four wheel drive vehicles.