Well... I have.
I think when I started becoming a kpop fan and also got into Super Junior, I think I had those thoughts too.
Like wishing that I had gotten into kpop earlier or that I was an ELF since their debut. (like I started stanning them 7 years after their debut)
For Voisper, I kinda also was like that. Even thoguh it was like some few months after their debut.
Or when I started stanning them, I remember finding out that they were in an episode of Immortal Songs 2 and won in that episode. And I remember wishing that I had stanned them before that episode was released. (probably so that I could feel happier when they won)
And for ATEEZ, I actually sometimes have these thoughts that are like "I wish I stanned them earlier" or wishing that I listened to Pirate King and Treasure when it was released. I think I pretty much didn't give a fig about them between 2018 and early 2020, and I pretty much also slept on a lot of their songs and stuff. (one reason behind me sleeping on some of their songs was because of me having the weird habit of putting a lot of videos in Watch Later and then forgetting about those videos until months later. I was also pretty busy with some other stuff back then.)
I didn't end up stanning them until I listened to Inception like 3 months after its release and fell in love with that song.
Sometimes I feel like it would have been more fun for me, if I was stanning them since debut or back when they were KQ Fellaz.
Well... I think Leeteuk once said to ELFs something like "It's okay if you weren't with us in the beginning. As long as you are there till the end"