Hi
A RDS CAL can be installed on a Server that has the same version or a newer version.
Ex: a 2019 RDS CAL can be installed on a RDS License Server 2019 or 2022.
A RDS CAL is backward compatibility.
Ex: A 2019 RDS CAL can issue CAL for a client that connect to a RD Session Host 2019 or lower version
Here is a compatibility between the Windows Server version and the RDS CAL that can be installed. Also, you may have your answer about the 120 dats grace period.