In the fourth episode of season 3 Sir Phillip reveals he has already written and published his memoirs up to this point ... which means Sourquill has been completely wasting his time writing it again. Given the nature of the programme, this may be intentional.
In the very first episode, Sir Phillip does say that this is the first time his true life story is told, and that while all his books have been based on, contained parts of, and offered clues to his real story, none of them have told the whole truth. So the memoirs he mentions could be incomplete or just plain wrong.
As of series 4, episode 3, all Ripely's memories of Pip are the ones "rammed back in" by violent physical contact with his autobiographical books. Given the questionable accuracy of the books, one has to wonder how much she really knows about her own life up to that point.
The dreadful event Pip is trying to stop at the end of Season 1 is Pippa being forced to marry Mr. Benevolent. Several series later she starts crushing on him, and then Pip follows suit. Is Evil Is Sexy a slow-buildup thing?
There are hints already in Season 1 that Pippa is nurturing a small crush on Mr. Benevolent. In the fifth episode, A Young Love Mercilessly Dismembered, after Pip and Harry barge in and save her from Mr. Benevolent while he's trying to steal a kiss from her, she agrees with Pip that it was a "horrible experience" — but then she adds "Although..." in a contemplative tone. Pip is quick to cut off further thoughts in that direction, but it does seem like Evil is pretty Sexy already here.