Vin numbers on big blocks

I have come across many big blocks and some have the hole vin number on them from what ever car they came out of but also some have half the number on them and some have no number on them.i was told the ones with no number were warrenty blocks and the blocks with all or half the vin on them depended what car plant thay came out of.does any one know for sure,just would like to know.