Have bypass cap recommendations already taken derating into consideration?
I would say as a general rule that data sheet examples and application note circuits are there to show you how to make something "work" however more advanced options such as making it work reliably under all conditions is left to you the designer.

The level of quality if app notes etc varies by vendor but you should keep in mind that the person who provided that schematic to you may not be as experienced an engineer as you, and may only have ever made circuits for eval boards and not actual production.  Or my personal favorite marketing may have had a say in scaling down the component values or quantity to make the solution look cheaper compared to a competitor...

In other words treat the datasheet and app notes as a guide and use your skill, research and hard work to make a quality product ;)

Edit---
I'd add to more directly answer your question that I'd bet most bypass cap recommendations don't even think about aging or derating and further probably are based on some outdated rule of thumb (again vendor dependent...). I'd recommend looking at what they suggest and then doing your own analysis.