Messages Deleted

This is something that happened a while ago, so while a solution would be nice, I’m really just wondering why this happened. My first phone in 2017 was a Samsung, and then I switched to my mom’s iPhone 6 in February 2019. My next phone was my mom’s iPhone 8 in December 2020. I don’t know when I realized this, but at some point I started noticing a gap in my messages when looking back. There would be something from January 2019, and then it would go straight to December 2020. I just recently realized it had to do with the timeline of when I switched to the iPhone 8. I find this very odd because nothing else was deleted in the transfer. All of my pictures and emails and everything stayed, but my messages were deleted. Last year in December, I switched to an iPhone 13 Mini, and that transition went smoothly as well with nothing lost. Is there a reason only the messages deleted, and possibly a way to get them back? I have pictures attached of how in the messages app, it shows some threads that ended during the timeline of the lost messages, but when I click on them, it only shows everything before February 2019.