Suppose an old closed question has an historical lock on it, making impossible to vote/comment/flag on any post.

What should we do if such questions have a high visibility but contains some outdated or wrong information? What if the answers of a historical locked question become obsolete? indicates that such questions should be unlocked (and potentially removed), but what about cases where most of the information is still accurate and useful?

For instance:

What are best practices that you use when writing Objective-C and Cocoa?

I think this post still deserves a historical lock as the information provided is indeed useful. Only little parts of it are gradually becoming outdated and still being hit every time one queries for cocoa best practices.

What should we do when a historical-locked question provides, say 85% of useful up-to-date information and 15% of outdated one?