Couple of questions
Is this the file name
OR
is this what showed up in the Title column of Calibre?
Also
What is the setting for:
Preferences: adding books:reading metadata (a tab): Read metadata from file contents rather than file name.
If that was NOT ticked, the correction of existing books may be real simple.
TEST ON 1 BOOK
in the Metadata editor: select the imported format on the right: then CLICK THE ICON NEAR IT WITH THE PENCIL That reads what is in the book
(note this will not work if you have done something that caused the book to update internals from Calibre: Polish, Embed metadata, Even saving from the Editor (T).
)