Maybe my attitude is wrong, but I've always felt the onus is on the Question asker to dictate that they've found the old answers and provide explanation to why they're no longer relevant to the problem. "I've already tried solutions from <x>,<y>, and <z> but they use functions depreciated in 2.1 and I'm using 3.0."
I do recognize the problem you're describing though. I think I've developed this mindset because I stopped helping out in StackOverflow a lot due to the low quality of many questions. I did a bit of time moderating with the intent to teach new users how to improve their questions, but ultimately the amount of users who want quick answers outpaces my patience so I just moved on. I follow two niche categories now that I consider myself an expert in and that's about all I help out with anymore.
Yeah, questioners should be encouraged to include version numbers. Ideally there would be a specific mandatory field for a version number. I'm honestly shocked there isn't one, it seems so obvious there's no way I'm the first to think of it.
I do recognize the problem you're describing though. I think I've developed this mindset because I stopped helping out in StackOverflow a lot due to the low quality of many questions. I did a bit of time moderating with the intent to teach new users how to improve their questions, but ultimately the amount of users who want quick answers outpaces my patience so I just moved on. I follow two niche categories now that I consider myself an expert in and that's about all I help out with anymore.