Create template "versioncheck" and prepend it to all pages starting with "Documentation/". The script reported below allowed to automatize the process.

You can now see a banner a the top of the "obsolete" pages guiding the user toward the appropriate set of documentation:
http://www.slicer.org/slicerWiki/index.php/Documentation/4.1/Modules/SimpleRegionGrowingSegmentation

http://www.slicer.org/slicerWiki/index.php/Documentation/4.1/Developers

// ----------------------------------
import mwdoc
doc = mwdoc.Documentation('slicer.org', '/slicerWiki/')
doc.login('UpdateBot', 'XXXXXXX')

Prepend documentation/versioncheck template. See http://na-mic.org/Mantis/view.php?id=2887

for version in ['4.0', '4.1', '4.2', 'Nightly']:
pages = doc.listPages('Documentation/%s' % version)
for page in pages:
text = page.edit()
text = '<noinclude>{{documentation/versioncheck}}</noinclude>\n' + text
page.save(text, summary='Prepend documentation/versioncheck template. See http://na-mic.org/Mantis/view.php?id=2887')
print "[INFO] Saving page: '%s'" % page.name
// ----------------------------------

Closing resolved issues that have not been updated in more than 3 months