When editing and saving a digital image, EXIF information can be destroyed if not saved correctly. But files may contain similar EXIF data known as maker notes.
Maker notes, however, are not standardized. Since they are proprietary they can not always be read by all EXIF readers.
More information about marker notes and the inherent problems with and mysteries of them can be found here.
EXIF Maker notes – Reference Information – find maker note tag definitions for digital cameras by manufacturer.