Is subdural hematoma possible after a head injury one year later?

See below: It's possible but is most likely healed.

Unlikely in young: In a young person, it is unlikely. In an older person (>80 years), the patient may have a chronic subdural hematoma. As we get older, the brain "shrinks". There is more potential space between the brain and the dura. Thus, small, often times unnoticed bumps on the head can tear the bridging vessels, thus leading to the sdh.

At one year following a prior head injury, there might be a diagnosis reached of a prior subdural hematoma, BUT new bleeding in absence of a new head injury does not suddenly emerge in absence of a hematological disorder or use of anticoagulant medications.