Added-to-library Field .. How to?

Hi, I do know that Endote make internal a MySQL DB. Ok, I can find all necessary fields in refs.* BUT WHERE is the ‘added to library’ Field? How is this date created in the Display Fields on the GUI? I need to get all added-to-Dates in an Result set. I can not find this field internally nor in a other way to get a Grouped-Info how many Records I have added on which date.  I would be happy and thankful to get some advices and help. Walter