Final answer:
The line 'for unto us a child is born' is from a pastoral poem and does not refer to a specific release date. It is not related to Jesus but instead likely refers to the child of Mark Antony and Octavia. Therefore, it is not associated with a specific year.
Step-by-step explanation:
The phrase 'for unto us a child is born' is a line from a pastoral poem which prophesied a golden age after the unrest of the Late Republic. This particular interpretation of the poem suggests that the child mentioned is not Jesus but likely the child of Mark Antony and Octavia, Augustus/Octavian's sister. Therefore, the line was not released in a specific year, as it is not a song or a piece of art but rather a line from a poem.