It makes no sense at all actually and this is why RW took care of saying they were almost sure, but not sure.. Imo, this decision to innocent Tannerman was partly a wishful thinking and partly untying a anti-productive knot that hampered any progress.
How do we know this is the reason Redwood says they're not 100% sure that Tannerman is being ruled out, Anne? They have not made their reasoning open to the public.
It would however be very interesting to know exactly on what grounds SY feel (almost) able to rule him out. Knowing their reasons would clear up most of the questions we have here.
SY are of course under no obligation to reveal their reasoning, but I wonder if it is reasonable to imagine that at some point they may choose to do so. Or it might come out some other way.
In the Barry George case, for example, there was a great deal of information in the public domain as to the reasons why certain things were being ruled in and ruled out.
Perhaps we can hope for this here.