HI, from what I have seen PETG is amorphous and not considered to have a crystalline phase. However, I am referencing an article that induced some small degree of crystalline phase into PETG by strain induced crystallization, Article Strain‐induced crystallization in uniaxially drawn PETG plates
. The PETG was drawn out and samples were looked at by DSC and x-ray diffraction. They estimated to have about a 3% crystallinity. If you are doing all the analysis with the DSC alone, assuming you have a crystalline phase to detect.... I don't know if DCS will be able to do it for you alone. Just an idea crystallinity can impact Tg, so you might get some relative idea of crystallinity by having relative shifts in Tg in your samples, but that would be more qualitative in describing any potential crystalline phase.