Jon's letter is purposefully unaddressed for a couple of reasons. One is that it's vague since Jon himself didn't have a very good or trusty source of news at the Wall, and later, when he did leave the Wall, the sources were just unclear already or hostile/dead.
Gladiusx
2023-03-26 01:06:08 +0000 UTC
I like Ned’s approach of, ‘Jon is most likely crazy…but juuuuuust in case’. At minimum even if he doesn’t truly believe Jon lived the future, he’s seeing that Jon’s words about Robb’s shortcomings (I’m assuming Jon included something about it in his letter) are true, and that Robb has taken the wrong lessons to heart. Very smartly done.