There are a couple of questions addressing what happens when you upgrade the minimum iOS of an app and there are still users on older iOS versions.
The answers don't seem to agree with each other. Some say that the user sees no update, but others say the user does see that there's an update available, but that she should update their iOS first.
To get rid of uncertainty, I was wondering if anyone knows if there's official documentation from Apple about this and where to find it?
update
The question here is an example of the question being answered, but only for the case where the device is actually capable of updating to the new iOS. The answer is also enlightening, but fails to provide any official Apple documentation on it.
This documentation might not exist (I couldn't find it), but I thought it worthwhile to throw the question out there.
Best Answer
Nope, not yet at least. Whenever my apps need an upgrade to their minimum requirements due to a new version of iOS, I always have gotten an email explaining everything.