Today I came accross an interesting article about keeping outdated incorret technical information around in form of blog posts.
I too see this problem and have to deal with it often enough myself when I'm googling for information. You can never be sure if what you read is still valid or just silly outdated stuff. It gets worse if the blog posts/pages don't contain any date where you could see when they've been created (because I learned the hard way to look for exactly that before I even start reading).
However, I don't see this as a reason to stop blogging about technical stuff alltogether, like the article suggests. The nature of technical blog posts (at least in my case) are often just quick hacks, or short code snippets which, most of the time, aren't worth updating regularly. In contrary to the author of the aforementioned post, I don't see the web as something which should only serve fresh and valid information and I honestly don't care if something I wrote two years ago doesn't apply anymore or people don't verify information they find on the web.
Also, if I'm seriously after valid technical information I tend to look for better resources like wikis and official docs of some sort. That however, doesn't apply to everyone who comes accross my blog so I decided to display a nice little info message above every post which is older than 100 days to inform the reader that the information he's about to consume might not be valid anymore
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I guess that should suffice.
I'd rather have important info dashed off in a blog than not at all. I do like your idea to flag old stuff to give readers a heads up.
It isn't just tech stuff, it can be political stuff that gets outdated too. Blog formats vary, and it isn't always easy to see the date; most themes seem to place them as inconspicuously as possible.
But there times when people want old news too. Sometimes even on purpose,