EDIT - The statutory construction and history clearly points to a literal definition.
Yes, I would interpret it literally. If you completed your bachelor in three years, then that was only three tax years in which you claimed the American Opportunity Credit. However, note that if you are claiming it for a fourth tax year, it must be for credit toward a degree (or similar credential).
Publication 970 repeatedly states the issue as "first four years." It never lists graduation or completion of the degree as the termination of the credit. It would be very easy for them to write somewhere in Pub 970 or in the Form 8863 instructions that completion of a bachelor degree ended eligibility for subsequent years. Take their words literally.
But again, note that you must otherwise qualify: expenses from a degree program, no drug felonies, at least half-time, and so forth.
EDIT continued - Please look to IRC § 25A(b)(2)(C) and § 25A(i)(2). The Hope credit was good for only two years. The American Opportunity Credit, passed as part of the stimulus/ARRA, points to the Hope credit 2-year limit but changes it to 4 years. No mention of degrees conferred or of moving into a different program. Please do not leave credits on the table.