Some things will be entered immediately at the point of publication, the same week. This includes things such as the Journal of the American Medical Association, or the New England Journal of Medicine, or Lancet, the 'premier' medical journals. For substance abuse journals there is frequently a lag-time of 9 to 12 months. In the absence of the above kind of information one can't evaluate the results of a particular database search. Determine the file structure.
Databases differ in the kinds of information that they include.
Typically there are different choices for displaying information. Some of this is irrelevant to anyone other than the library staff, but it provides the most complete picture. When exploring any new database, print out a few citations in the longest format available. This will be useful later in deciding how to search for materials. At other times it can be a treasure trove.