That is the correct spelling of "retrospectively" (seen in hindsight).

Retrospectively, I can see where we went wrong.

The principle you are looking for is that a law may not be implemented "retroactively," not "retrospectively." This principle means that you cannot implement a law, and then apply it to cases that occurred before the law was implementd.

reference to the sources of south african law,discuss the principal that law may not be implemented retrospectively

It depends on the religion in question, but in Catholicism the godparents are the witnesses to baptism and you can't retrospectively change who witnessed something.