Updates are not limited to only one or two time. But it’s important to fairly give every civilization chances to having updates, and strike a reasonable balance between the game’s entertainment, historical accuracy, and acceptable development costs.
On the other hand, the Germans, Indians and Native Americans, their respective issues are actually quite different. Comparing them won’t do any help to improve the status quo.
About the Germans:
It’s a bit outdated due to the release of the new DLC, but the concept may be still good.