Forms :: Old Value On Update

i have two forms one releaseorder (master/detail) and second stock query (single table)

when the user enter the detail table like container no one or more rows then it will insert the rows into stock table through post insert but if need to change the multiple container no then it will only update the one container no where cursor available through post update how to update multiple container no in stock table should i try copy container value to display item or :global.old value.