IMSI and IMEI in A/Iu CS interfaces

Hi all, i maked some A and IuCS traces and i observed that in gsm traces few IMEI and IMSI were sent over A interface, but in IuCS ones the number of IMEIs is much higher compared to the number of present IMSIs which is lower than the one of GSM, is this normal behaviour? Normally the number of IMEI should logically equal the number of IMSIs present in 24h capture?

Any comments plz.