Well, this site is about "German language & usage" but it does not state that it must be contemporary German. And any reform is related to the language and its use.
That said, it's likely a little difficult to answer questions about things in the past. Most of us will still remember the most recent reform but I'm sure none of us experienced any prior reforms. That is, only those who studied the history of the German language will be able to answer such a question properly. Therefore, you might be more successful in getting satisfying answers if you ask any questions like those on our sister-site about linguistics as I assume that there are more 'experts' when it comes to history. I'm not sure if they define those questions off-topic though.
However, this does not make a question off-topic on GLU as long as we do not expressly exclude those per definition. And I think we shouldn't go so far. Perhaps such a question will lead some experts from linguistics over to GLU some time.