@RadioDave the benchmarks will repeat. Ain’t No Sunshine has come up on these dates: 9/8/24, 1/14/25, 5/13/25 , 9/9/25, 1/19/26 ~ every 4 months.
If you desire, you are free to play the song or do some the challenges as an exercise or warm up or whatever you please. TAC gives you the freedom to use what you’ve learned in any way that tickles your fancy. I have certain ones that I have enjoyed playing and have repeated a lot throughout the year, usually on my TV couch when nobody is listening but occasionally with my wife next to me.
Of course, which ever chord progression that you repeat more often will stick better and you will find it easier when it comes around again. But if you just do your best each challenge day, you will move forward, no more is required. If you are enjoying yourself with whatever you are doing with your guitar, you should keep doing it.