Good Day Scott,
Nice to see you around on occasion again.
So, First, the "For beams that are specified in the contract documents with camber" does not indicate those members ordered by you from your steel supplier. That refers to what the engineer has specified for the condition of the member when shipped by the fabricator to the job site. As such, if it came from the mill and steel supply with 75% of the specified camber it is okay as received by you.
Thus, Your member could have arrived with a 3/8" camber and you would not have to add any camber to it. Since it is only 50% or 1/4" camber you need to add more camber. The allowable tolerances would now be -0, +5/8" (1/2" over for the first 50' and 1/8" for the additional 9'-3"). So it can be camber from the specified 1/2" to a total of 1 1/8".
Now, having looked at AISC COSP, note that as the applicable working code, D1.1 would rule. So, as you didn't say anything about it being embedded in concrete, I would be looking at Clause 5.22.3. You have specified camber but not with concrete haunch. So, for your beam length, -0, +3/4". Since your specified camber is 1/2", now you can be between 1/2"-1 1/4".
The COSP is a reading of STANDARD PRACTICE. It does not necessarily dictate the final conditions to be adhered to. But, the applicable code, in your case D1.1, does give us just a slight bit more latitude in camber but pretty close to the standard practice from COSP.
Hope this helps.
He Is In Control, Have a Great Day, Brent