Sometimes old answers were correct at the time they were written, but the march of technology has made them obsolete. 

For example, the command-line video encoding tool ffmpeg used to have a 'vhooks' function, but that has been replaced by an entirely new syntax, making [this](https://superuser.com/questions/86760/mass-convert-videos-to-flv-format-with-watermarking-in-windows/85350#85350) answer incorrect for all recent versions of the program. However, when I flagged the answer as such, my flag was rejected on the grounds that

> 
> flags should not be used to indicate technical inaccuracies, or an altogether wrong answer 
> 
> 
> 

So my question is: what is the correct response to this kind of obsolete answers? Downvote & leave a comment? Edit the question to correct it (would seem to be little too drastic a change for an edit)? Something else?