Is Wikipedia's table about SHA-2 collisions correct?
No. The wikipedia article is in my honest opinion misrepresenting this article on a reduced round attack on the SHA-2 family of hashes.


  Although these attacks improve upon the existing reduced round SHA-2 attacks, they do not threaten the security of the full SHA-2 family.


In other words, no collisions have been found in any of the SHA-2 hashes.

The numbers that the are shown in the table mean different things for SHA-1 and SHA-2. In the case of SHA-1, the theoretical attack finds a collision in the actual SHA-1 algorithm. In the case of SHA-2, the collision is found in a modified algorithm with only 24 of the normal 64/80 rounds. In practice, this means that the best collision attack against SHA-256 still has the theoretical upper bound of $2^{128}$ complexity, and the best collision attack against SHA-512 a $2^{256}$ complexity.