Do You Remember, 21st Night of September?

HAPPY SEPTEMBER 21st! Crank this funky diddy and start dancing in your office. Today (Tuesday) is the final FULL DAY OF SUMMER 2021!

Do you remember, 21st night of September?
Love was changing the mind of pretenders
While chasing the clouds away
Our hearts were ringing
In the key that our souls were singing
As we danced in the night
Remember
How the stars stole the night away, oh yeah

Holding hands with your heart to see you
Only blue talk and love
Remember
How we knew love was here to stay
Now December
Found the love we shared in September
Only blue talk and love
Remember
True love, we share today

"September" was a #1 for Earth Wind and Fire in the late-1970s.

What's so special about that date? Why was that date chosen as the lyric?

Vocalist Maurice White claimed he simply chose the 21st due to how it sounded when sung. But his wife has claimed that September 21 was the due date of their son. But their son, Kahbran, ended up being born early on August 1, which definitely wouldn't have the same ring to it as a lyric.