In Scrum and/or other Agile methods how do you handle versions of requirements simply? I assume that there are plenty of organisations who are Agile but also need to keep a track of requirement changes for regulatory purposes and so on.
You may have a requirement in version 1 which is substantially altered in version 8. How do you track that kind of change between releases?
The simple answer is: we don't, as keeping track of the changes doesn't usually make much sense or bring any benefits.
However, if for any reason you must keep track of changes (like wasteful overhead forced upon you by "regulations" - not unheard of, right?) the best thing to do is to keep your backlog in such a way that you would be able to tell how and when it did change. This is where scrum software tools can help, as doing it with a board and index cards would be a major pain. Sometimes just a simple history of all changes to any backlog item (like what we have in our Scrum tool) will suffice, sometimes you will need more complex reporting (available in some more complex tools), and sometimes you will have to produce some additional documents.
BTW - I understand "a requirement" to mean a single backlog item, usually a user story (or epic). As such those usually don't change a lot, their position on the backlog does, but usually not the stories themselves. Recording changes of stories position on the backlog doesn't make much sense in an agile project, however recording when stories were done (keeping data about past sprints) is a good practice. Recording changes to the story itself (edits, changes of attachments etc.) would be where the Scrum tool should help you if this is what you want/have to track.