Different narrators have different levels of reliability (a wholly separate issue from quality of writing).

IMO, JA as narrator is very reliable, I take what she says as truth if it is from the omniscient point of view. But JA also moves from omniscient to a more personal POV; in Persuasion, that of Anne or occasionally FW. When you are in a more personal POV you are subject to that individual's limitations--s/he does not know what others are thinking, and (ahem) he may not even be aware of the truth of his own thoughts and feelings!