It's the same problem a lot of internet properties that crowd-source data have now, which is that they don't have the concept of time and knowledge degrading over time built into them.
For the first 5 years or so, Stack Overflow was amazing. For newer subjects that haven't changed significantly in a the last couple years, it's probably still amazing, but the shelf life on this is much shorter in general, because new subject generally change quite quick (conversely, when Stack Overflow was first filling up, all the C/C++.Perl/Python/Bash etc stuff were long past their high churn stages).
When all these sites were new and shiny and still filling in the gaps, this wasn't a problem. Now that we've gotten a decade or more of some of them, they have the problem of being filled with information that was highly relevant at one point, but as it's lost relevancy over time is still treated as relevant.
As the timeline of major changes to these crowd-sourced repositories of knowledge goes, I think the next major advance will be a good algorithm to degrade relevancy (points?) over time with the ability for people to "vouch" for data as still accurate, or to "refine" data to limit the scope it applies to when the subject has expanded and it no longer is as accurate as it was because of that.
E.g. an answer for a Python which works only for Python 2.X but at the time applied generally because Python 3 had not been released. After Python 3 comes out, that answer either needs to be less relevant because it's only sometimes correct, or refined to note where it does and does not apply, in which case it retains its relevancy and should hopefully not crowd out data for the portions of the subject it does not apply to (Python 3 in this case).
I'm convinced this, or something like it, is the next big thing for crowd sourced data, as it becomes more and more important as our collective online data ages.
Edit: It's worth noting Google has likely already solved this, at least for their problem space. Then again, the way Google could be considered to be a repository of crowd sourced data is slightly different than most sites. That said, I wouldn't be surprised to hear they have a solution, either in place or planned, for how to deal with this affecting the knowledge graph.