Lost Worlds after December 2019 Upgrade

I'm a windows user. On or around 10 December 2019, my boys were unable to access any of their worlds. I have since located all of their worlds in the following directory on our computer:

C:\Users\Owner\AppData\Roaming\.minecraft\saves

The interesting thing is that the last modified date is 10 December, which I believe is when there was an upgrade. My boys gave up and created new worlds and now play daily. But there are NO files modified after 10 December in the above folder. So is Minecraft pulling from a different folder now? How do I point Minecraft to the above location, or copy the files to the right directory?