1, Most of pagings are done on TMSI but sometimes they aer done on IMSI which is named global paging and is done on MSC level not on LAC level(it occurs when the MS doesnt reply the message from the MSC in a special LAC, may be the MS is out of coverage area or the battery charge is finished or MS havent done a LU while has gone to new LAC in same MSC).
2, The times of paging can be set by the operator and normally the limit is different according to the vendors