Hi! Thank you, and I come with answers. Sirius does know all of his mistakes now as he tells the story, but as he goes through, he is honest about what he felt and thought at that time. So for a part of it, he's convinced that Remus has been unwittingly turned due to his 'compromised' nature as a werewolf, that scene at school is Sirius's thinking during the war, when he believes that Remus had been used by the Death Eaters while a werewolf, and revisits earlier conversations in light of this belief.

Similarly, Remus trusts Sirius implicitly at first, but becomes convinced that Sirius has been somehow led astray by his desire to protect Regulus -- or at least to get his body back or information on his fate, because both of them know the traitor has to be someone close to them, and neither of them is able to believe James would do it, nor that Peter is capable of it. Which is I think the central tragedy of their story, because if they had simply talked clearly and confessed their suspicions, it would have become obvious that it was Peter -- that's true for canon Sirius and Remus, too, even though the conversations would have been a little different.

Remus's fake job interviews are based on the canon covert missions Dumbledore sent him out on for the Order of the Phoenix, which we know he was meant to tell no one about.

Alas, if Sirius as narrator had been clear about every time Sirius in the past had been wrong, much of the story would have been 'And then I did something ELSE stupid …'