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When they differ it's often because another module's transaction created them. For example (might not be strictly correct) if a shipment is created on business date 1/24/16, it will create a corresponding timInvtTranLog with that date, but the shipline related to it, might have a specific shipdate set for it that is different than the above, e.g. 2/1/16. The timInvtTran created during posting of the shipment will have the date of the line, while the timInvtTranLog will have the date of the tsoShipment record.