IT loads are a pain. If you use the nameplate value on each server (or its power supply watt rating), you will have way more capacity than needed. Server racks usually have a PDU with a given power plug. I'll pick which PDU type I want based on certain things. If an L6-20 PDU doesn't have enough juice, I may ask for two of them. Or maybe an L6-30. The contents of that server rack will most likely change often, so even if you have an accurate load, it will be different in 6 months.
When our server rooms are inspected, the server racks are never there. All the inspector is looking at is the branch circuit to make sure all parts are correct, and not the load. Even if he saw the server rack, I doubt he could come up with a load easily as half the nameplates may be obscured, and nameplates aren't a realistic measure for most server installs.
One thing to watch is servers with redundant power supplies. If it has two 700W power supplies, and the computer is maxxed out, each supply will draw 350W. If one supply dies, the other one will provide the full 700W until the dead one is replaced. So this could be where the "half" comes from, as a computer with two 700W supplies won't draw more than 700W. The point of redundant supplies though is to have two separate branch circuits so circuit 1 powers supply #1 on each machine and circuit 2 powers supply #2 on each machine.
