Our card stacks on persistent news concepts are inevitably going to change over time. Some of that will be because of new developments in the world. Some of it will be because we've made mistakes. And some of it will be simply that we thought of ways to make the content better. For example, after hearing back from readers I decided to redo this chart with a clearer color scheme.
This leaves us with a quandary: how to be transparent with the audience about changes will still creating a great card experience.
What we decided is that rather than clutter cards up with lots of special marks and a whole bunch of extra text at the bottom of the page, we would add a whole changes card to a stack once it's modified. That way curious readers can get a rundown of all substantive alterations that have been made, while people who are just looking for a clear presentation of information will have it.
In the longer run, we'd like to create a somewhat more technologically elegant solution to this problem but this seems like a good enough approach for now.