Your assumption is based on the three stages that he supposidly went through. The Ibanah was written according to Ibn Kullab's method as Ibn Hajar said, to strenghten that the Hanabilah rejected this work as Imam Dhahabi writes in Siyar. The Ibanah we have today has been corrupted, for example, Ibn 'Asakir quotes from Ibanah sayind 'Ayn (singular) while todays printed versions have 'Aynayn (dual). Much more differences refer to shaykh Ghawji.