Date A Song Was Written
Songwriters create compositions which include the melody, chords, and lyrics (if there are words).
Compositions exist without recordings although you can use a recording to help others hear how the melody and chords sound.
The date you completed your composition is the date you completed writing your melody, chords, and lyrics if applicable. Recordings and production come later. It is ok if you don't know an exact date! Just pick one that is close to when you think you wrote the composition.
Artists and Music Publishers will use this date in their searches for the perfect song. They may want a song written within the last year. Similarly, a publisher may be looking for a song written in the 80's because that is what a movie company is looking for.