A work can enter the public domain in many ways.
The following is a list of works that enter the public domain in 2012.
No whole man may enter my domain, save only the king.
Most of the activities are covered by the local media, and enter the public domain.
Most of the technology is developed in the military and quickly enters the public domain.
Nothing had entered my domain in all these years except those things that I brought here myself.
The correspondence will enter the public domain in 2017, 70 years after her death.
Unless the law changes, Graham's work will enter the public domain in 2061.
We were both working on radar, though that name had yet to enter the public domain.
The reality is that even things published decades ago will not enter the public domain in our life time.