We don't use work order or MRP, nor do we reference sales orders on our POs.  I've never had issues with the sales orders not showing up on tab 6 & the only problems I've had with incorrect data showing on tab 1 are cleared up by rebuilding the sort files. We do use bill of materials, though, and I would not expect it to fix any of the problems you are describing.

An item On Work Order means that it is being produced as a result of a work order.  Required for WO means that it is a component on a work order.  There is no way that an item would be the same.  For example if you had a valve on a work on and the parts are body, ball, stem, end.  The Valve itself would be On Work Order while the ball and stem would be Required for Work Order.