If you are concerned about changes in tensile strength to the flat bar that was required to be stress relieved at 1202 deg F (650 deg C) versus normalized, I would perform hardness testing. Hardness testing of certain steels can provide an indirect correlation to tensile strength. Comparison of hardness data should enable you to evaluate the affects of normalizing versus lower temperature stress relief heat treatment.
Select a sample of flat bar, prior to cold bending, to obtain a baseline hardness. After cold bending, perform the stress relief at 650 deg C, and conduct hardness testing at a location adjacent to and away from the outer radius of the bend on the flat bar. Perform hardness testing at the same locations on a second flat bar after cold bending that you suspect was heated to 850 deg C to 900 deg C, and air cooled (normalized).
If a normalization heat treatment did occur it should result in uniform hardness adjacent to and away from the outer bend radius of the flat bar. The hardness of the normalized flat bar away from the bend may also be affected, which is the reason for obtaining the baseline hardness. The flat bars that were cold bent and subjected to only a lower temperature stress relief operation should see some variation in hardness along the outer bend radius.
I would strongly suggest you send out your test pieces for hardness testing to a reputable metallurgical test lab.