Knowledge creation and knowledge sharing need to go hand in hand with knowledge retirement.
|Image from wikimedia commons|
However this means that someone needs to take this role. Although you can set up systems for the knowledge workers collectively to contribute new knowledge as part of their jobs - lessons learned, for example, or innovative work products - it is much harder to set up similar systems whereby people retire obsolete knowledge. It's better to appoint an individual to do this housekeeping task as an occasional task.
However you do it, the retirement of out-of-date knowledge needs to be part of your KM program, to stop your repositories and knowledge bases clogging up with too much stuff.