At least when I open a book today the pages are all the same as yesterday.
That's not always true with the internet.
In 2011 a search on Google Books resulted in a match for Erasmus Trautvetter in an apparent 1830 era German directory. I have tried on an off and on again basis to obtain a photocopy or scan of the relevant pages, but apparently accessing this book (which I've only been able to locate in a card catalog at Harvard University) is not the easiest thing in the world to do.
When I performed a search on Google Books today for Erasmus Trautvetter, the reference to the 1830 directory did not come up. I have not had time to really delve into the reason, but I'll be saving in some way, shape, or form results I am really interested in from now on. Regardless of the reason why, the inability to locate the Erasmus Trautvetter reference again makes the point that saving search results is important, especially if one does not have the time (or is unable) to locate materials referenced in Google Books.
And if anyone has access to the book, feel free to contact me.