You are propably wrong here, It is of course possible that there are "real" databases somewhere but chances for that are fairly slim. I have searched the device for that kind of data quite thoroughly and tracker DB's are the only thing I have found.

You are propably thinking of this sentence;
"- Tracker is an indexer that doesn't touch your data in any way except for reading it and allowing other programs to read it; the team behind it have worked real hard on making it as power efficient."

That refers to the way tracker indexes images, sounds and movies on the device.

However, as far as I can tell, when you receive a SMS message, the message is stored in tracker DB only, there does not exist any other private storage for messages.

There is one difference, however. For MMS messages, the active content, being sound/picture/video is extracted from the message and stored on a directory in the device FS. The text content of the MMS is still stored only in tracker.