1832: It seems that in this account, Joseph is painting with a broad brush. This is a first draft, I'm thinking, and so contains chronological inconsistencies.
My current work in progress is an exploration of what difficult life experiences and the word of God have taught me about the difference between codependency and ministry. I have found that my initial memory of significant events is not entirely reliable. Understanding I acquired in the school of hard knocks bleeds back into my perception of my previous mindset. It takes conscious effort coupled with a review of journals and my reasons for making the choices I did to untangle what I know now from what I knew then.
I think I see some of that same tendency in the 1832 account of the First Vision. Here, Joseph recalls having come to a conclusion that the world was in apostasy and his primary motive is to get a forgiveness of his sins. This contrasts with his later account, where he says that it had never entered into his heart that the churches were all wrong together.
I feel like in this account, the things Joseph was soon to learn colour his recollection of his state of mind. For instance, he talks about how he noted the hypocrisy of those who professed religion. My guess is that he didn't note that hypocrisy until after he shared his experience with the Methodist minister whom he admired. Perhaps that influences his dating. He remembers his 15-year-old mindset, and places the First Vision at that time, rather than earlier. I also wonder if there's a confusion of his recollection about his state of mind at the time of the First Vision vs. his state of mind right before Moroni's appearance.
For me, these inconsistencies are a mark of authenticity, because of my own experience of misremembering. It seems like the functional memory (I don't know if that's a real term, but I use it to mean the quick-recall memory that informs my daily choices) is not focussed on chronological clarity. So a first-written memory of such a transcendent event as the First Vision would be expected to be out on some details and possibly conflated with similar transcendent and formative events in his youth.