[Adoby]

The metadata, like the name of a book, is stored in many places.

In the calibre database.
In the folder name for the book.
In the filename of the book.
Inside the file that is the book.

When you change the name of the book in calibre, everything but the last is updated. Calibre doesn't update metadata inside the book, unless you explicitly ask it to. This can be done by converting the book to the same format, for example epub to epub. Or you can "Polish" the book or use the plug-in "Update Epub". When the book is saved to disk or sent to device, the insides of the book is also updated.

So the books that are inside the calibre library are usually not updated to reflect what the calibre GUI says about them. That is one reason why it usually is bad to even peek inside the library folders.

The reason is that it is expensive to change the insides of a book, and also it may cause loss of information. This way there is no need to ever change the book in the calibre library. The contents of the book can be kept exactly as it was when it was originally imported.