Another thing to consider is the 'kidnapping' of Lyanna and how Ned might feel guilty about it.
We now have reason to believe she was taken near Harrenhal.
We also know that Brandon was relatively in the vicinity; tending to the post-duel errand and then headed back up the Kingsroad to meet Rickard.
Would Ned have been in charge of watching his sister at some point? Maybe he left her in the guard of the Whents, so that Ned could go to see Ashara? Or Ashara was at Harrenhal (though I can't think of a good reason why)? Or there was a Brandon, Lyanna, Ashara, and meet up for conversation?
Was Ned supposed to hand Lyanna off to Brandon and Brandon did not show up?
Ned wanted to head up the Vale to visit Jon and Robert. And we know that Ned was at that time either in the Vale or en route to the Vale.
It was likely a style choice for the AGoT prologue to not let Will have an inner monologue. But then GRRM just gave up in later prologues, because writing 'correctly' can read as very wooden and far too different from the rest of the books, which the AGoT Prologue does.
Ultra-fine aspects like these will almost never come out in the books themselves. It would have to be GRRM saying, "I meant Will as an homage to Shakespeare," or "That time I switched to 'you' was an indication of magic," which is kind of lame to have to tell your readers what you wrote, as opposed to having written in the first place.
A great example is the "Prometheus" film from a few years ago, the creators went on and on and on and on in the press after the fact explaining the story and what they tried to say, which only revealed that they did an incredibly poor job of telling a story in the first place.
Will does not get the benefit of italicized inner thoughts/speech.
If you compare to say, Cressen, in ACoK, he does get he italicized inner thoughts/speech.
At the time of the first book, perhaps they completely avoided the inner thoughts for Will for whatever reason.
Within Will's prologue the usage is consistent, which separates it from the rest of AGoT. It is only in the later books, with other Pro/Epilogue, that do get italicized inner thoughts/speech that the writing of Will seems odd.