And in any case some images comparing the two could lend some credence to your claims.
I certainly do not consider this a QC issue, it is a slow film issue. Efke 25 behaves similarly. I have seen that if it sits around and isn't developed promptly the images are less dense. I suppose it could be my storage conditions, (cool but not frozen - I don't have those special thermostatic hands) but what I see for myself I tend to believe more.