Definitely agree with your tldr, there's some responsibility on the reader side as well. Even when authors don't declare their expertise, the context of the information, which might just be its age, can often be enough. You should know what you're getting when you read and take examples from the old PHP doc commenters, for instance.

I was setting up emacs + evil mode the other night to give it a real spin for the first time, one blog post from 2014 was pretty helpful but I suspected I'd have to throw out a bunch of things (if they worked at all) as I got further along and learned more about the ecosystem. Sure enough the way people add packages has changed, but this blog author helpfully updated the post in 2016 with the new information (and left the marked-as-old info there for context).