This switch happened in the 1930s or early 1940s; however, the exact year is not clear.

He lived to a great age, but the exact year of his death is not recorded.

The exact year of the battle is likely to be unknown.

The cabin was most likely built between 1638 and 1655, but the exact year is not known.

It was built in the 12th century, however the exact year is not known.

The exact year of the building's construction, and its original purpose, is not known.

She died before her husband, but the exact year is not known.

The period started in the 1910s, although there is no exact year.

The exact year and place of his death are unknown.

I can be flexible when it comes to the exact year.