Thinking about this crazy year got me thinking of what it will look like in our textbooks. How long does a textbook writer wait to write about current events? What is the process? Are there rules of thumb like "shouldn't teach the target audience something they would have remembered happening"? Is something more likely to show up in a textbook in less time because "decades" are published together?
Although it doesn't directly address the question about textbooks, this rules explainer might be an interesting place for you to start as it covers when "current events" become "history."
Likewise, it doesn't exactly get at your question but my answer to a previous question, Who decides what goes into history textbooks and what doesn't? might shed some light on what you're asking.