Don't know about efficient, but there is at least two ways which seem to work OK-ish (although not all that efficient, I gahter):

* Do regular certifications. Before certification, check if the document is up to date. If not, update it.

* Share the documents to answer teammates' questions. Like with a WIKI it may turn out that the important stuff is actually missing/undocumented/outdated. This is then a good opportunity to fix the document.