coe and sag point and annealing point

There is no direct relationship between COE and sagging and annealing temps, although roughly, the higher the COE, the lower the temps, as shown most clearly with Pyrex with a low COE and higher temps. Absolute COE is a laboratory process involving precise temperature control and measurement and a certain amount of fudging in the case of fusing because the measurement is done well below fusing temps (max 300C). COE can also be calculated from the chemical formula, giving a different, but predictably different, answer. Relative COE is much easier and is the common test described in books - fuse or melt together two pieces of glass and look at the result through a polarizer and if there are no strain lines they have the same COE.