When a Remote Desktop Session Host (RD Session Host) server is configured to use Per Device licensing mode, and a client computer or device connects to an RD Session Host server for the first time, the client computer or device is issued a temporary license by default. […] If the license server is not activated or does not have any RDS Per Device CALs available, the device continues to use the temporary license. The temporary license is valid for 90 days.
A permanent RDS Per Device CAL issued by a license server is configured to automatically expire after a random period between 52 and 89 days, at which time the RDS Per Device CAL returns to the pool of available RDS Per Device CALs on the license server.”
Meaning that after replacing a device, the RDS Device CAL will auto unassigned within 52-89 days. During that period the replacement device will have a temp license in place for 90 days. When the RDS Device CAL is unassigned from the old device, it's added to the pool again and therefore also available for the replacement device.
Check this link please - rds-client-access-license
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