For an example of this, ask yourself: What is the world population?
The longer it has been since you checked, the further off the number will be.
The longer it has been since you checked, the further off the number will be.
The need to reread and reconsider books, ideas, etc. is not to check if the facts have changed, but to make sure you didn't miss a point because of lack of knowledge or bias.
For example (on a very basic level), I find that if I reread a book on a programming language after using it for some time I notice things which I missed on a previous reading or wasn't able to appreciate due to lack of familiarity with the language. The same can apply to history - or any other study - where one only appreciates certain details after understanding the larger picture and surrounding events.
For this reason there lies an advantage in both rereading the same book (immediately or after some time) by itself and reading after studying more on the topic from other sources.
And then, when you finally accept that you don't grasp it and start calculating with a formal growth rate, the growth rate suddenly changes.
[1] Nobody does. Some people know they don't, some are completely naive, the others lie to themselves. The first group have a chance of dealing correctly with it.