Concrete Sky was created on 2002-07-16.
Across the Concrete Sky was created in 2003.
No, sky is not a collective noun; sky is a common, concrete, singular noun.
Yes, the noun sky is a concrete noun, a word for something that can be seen; the sky is the visible image of the air molecules in the atmosphere. A concrete noun is a word for something that can be experienced by any of the five physical senses; something that can be seen, heard, smelled, tasted, or touched.
Concrete Law was created in 2001.
Concrete Blonde was created in 1982.
Concrete Igloo was created in 2005.
Concrete Rage was created in 1993.
Concrete Rose was created in 2003.
Concrete Mathematics was created in 1988.
Eugene Concrete was created in 1979.
Concrete Cowboys was created in 1979.
Operation Concrete was created in 1955.