This sling brings up some information that I recently found. I have one company and one company only, that used the Klikit Pull fastner from Rau. It was E. A. Brown, in RI.
However E. A Brown had a late contract of OD slings. E. A. Brown also did not use this type of C clip. This style has the "advanced and decorative" design in the middle. I have never seen that one a US GI sling before.
The sling may be legit, with somebody either in the service, or a dealer changing the C tips. C tips, no matter how much we love them for their historic nature, were very bad for the user. The popped loose, got bent, and often just slid off the fabric.
Without actually handling the sling, I cannot tell you anything about it. This one, if it is US GI, is an exception to every known rule.