1) Carolyn's age. I think the first time they fudged on that was long before the Leviathan period: it was when Elizabeth was telling the story in 1968 of Paul last night at Collinwood. It seems to me the idea was that Carolyn was already born when Paul quit the scene.
Ah, yes - that's true. Now that you mention it, not only does Paul indicate in the '67 flashback to '49 that Carolyn is two (which jibes with Leviathans), but I seem to recall Jason laying it on thickly while telling Carolyn how much Paul loved her. Though in my defense, and as I and others have opined on the forum, some of us have tended to think of the dating in that storyline as an aberration if only because it conflicts with most of what came both before and after it. As I and others have also mentioned on the forum, our rule of thumb when it comes to inconsistencies on DS is to go with what's mentioned most often, and in most instances within the storylines the indications are most often consistent with Carolyn being 17 at the start of the series. (And actually, another thing that's odd and aberrant about the Jason/Liz blackmail period is the listings in the family bible because the ep in which Liz writes in the date of her death aired in July, yet Liz writes the month/day of her death as April 10th. That's the only time in DS history when a month that's somehow referenced on the show doesn't correspond exactly to the month an ep actually aired.)
But, after establishing that she was 2, they make sure to show Paul the picture of Carolyn as a young girl (I think they say 8 years) and then he sees the girl and tries to follow her. Of course, the picture could just have been how she looked at 8 after he had been gone for a while, but I think it was indicated or implied that it was how he would have remembered her.