There are thousands of old questions on SO that got migrated a long time ago and don't add any value to the site. These questions should be deleted. Due to the recently added redirects of deleted migrated questions, users following old links would even be redirected to the new home of the question.
The easiest way to handle this would be an automated task. Some period of time after the migration (like a month or two weeks), the migrated question should automatically be removed.