As verbs the difference between overtitle and overcrowded

is that overtitle is to give too high a title to while overcrowded is (overcrowd).

As a noun overtitle

is (chiefly|in the plural) one of a set of lines displayed above a stage and manually synchronized with the speech of the actors, rather like television subtitles.

As an adjective overcrowded is

containing too many occupants for an area of its size.