calibre contains separate fields for "titles" and "series". When saving an e-book (to an e-reader or storage location) , you can instruct calibre to merge "series" and "title" to form one file name like "Lord Of The Rings 03 - The return of the King.mobi".
As some e-readers do not use the actual file name, but rather the internal tags, serie information can be presented differently, perhaps unusable. Hence, to overcome this, many users tend to add the serial information directly in "title" field, such as: "Lord Of The Rings 03 - The return of the King". In this way, e-book names are neatly sorted, and useable on almost every e-reader.
However, this presents problems when automagically trying to enhance meta data as due to the series prefix ("Lord of the Ring 03 -"), the chance is great that the title cannot be found anymore by the metadata databases. Further, the same series info is now to be maintained in two locations.
I tend to temporary strip the series prefix info from the title when updating/adding metadata, but that is tedious work. Is there a better way to use the existing "series" and "title" fields, but yielding the same effect?