The PINs will expire if they are not used within an activation time frame. Please see the guide below.

One-Time PINs must be used within 24 hours after creation

Permanent PINs must be used within 24 hours after creation

Duration PINs must be used within 24 hours of start time 

Bluetooth keys must be claimed within one hour after creation

PINs should just be in the Inactive tab after they have been used or after their expiration date.