HLR doesn't store timestamps e.g. of last subscriber activity
It would be useful for monitoring etc. if we had a 'last active at' timestamp or the like.
Last activity timestamp is critically important for commercial networks who need to recycle SIM cards or phone numbers. This recycling is normally performed based on the inactivity time which requires activity timestamps to be stored. E.g. that's the case for the network we're currently installing in Palau where there is a significant customer churn due to tourists, while numbering capacity is very limited.