PVO CstStdCostDetailsExtractPVO uses incremental filter that ignores some changes

Summary:

1] When multiple tables are joined to form a PVO, why is only one table's last_updated_date used as incremental filter for the entire PVO? 

2] What's the design idea behind this, and what's the suggested best practice to use these PVOs?

3] Is it possible to use max() of the two Lastupdateddate columns in this PVO as the incremental filter? 

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