You have a strange idea of how hierarchies work. Rowley perhaps could have sat in his office ploughing through all that information but in my opinion he did no such thing. He had underlings who did that and wrote reports. The underlings were looking for lines of enquiry relating to abduction because of the remit. Above all, they 'knew' 'Kare and Gerry' were in the clear. I expect he was known to them as 'Mark'.
I'd be surprised to find Rowley was permitted access to the files. I'd be surprised to find his job description requires such access. I would expect him to rely on executive summaries, with occasional briefings, but otherwise to be pretty ignorant of the details.
I don't see him having interest in fine details, nor having the time to wade through them.
The Manhunt programme suggests the person most in the know re OG would be DCI Redwood, but I doubt very much that he himself read the details. There were staff on his team to work in particular areas then procedures to assemble the results. In Manhunt, a clear example was CCTV. Sutton did not plough through it himself. He had several officers do that, and relied on the ability of his staff to flag up items of interest.