We have captured A interface and saw exactly the value of IMSI.
other informations are also available : old MCC + MNC which comes from our network but the LAC value is from another network ( unknown network ).
We print (with NSS guys) , the state of those IMSI in the HLR but we’ve got same results : IMSI not connected. But all those IMSI are registered in AuC Center.
NSS guys told me that it can may be numbers that have been deleted because of subscribers not having done any “cost activity” for 3 months..
My problem is that i am BSS guy and I need to reduce SDCCH signaling in order to avoid congestion.