A/P Invoice J.E

In 3 A/P Invoices i have these type of entries , are these correct . Why is it showing differen in all 3.

Customer1 452443

input cst 2%

goods received but not in 0

stock in hand 442860

purchase offset A/c 8857

purchase domestic 8857

cartage inward 726

Customer2 255575

input vat 5 13310

goods received but not in 242000

loading charges 265

Customer3 318152

inout cst 2 0

goods recived but not in 282786

stock in hand 6238

purchase offset a/c 6238

purchase domestic 6238

incoming cenvat clg a/c 29128

I want to know in 1 & 3 why it has created purchase offset , & in third one it is showing very less amount in stock in hand & purchase domestic.

In first stock in hand has big amount. What is the reason

Thanks