I think it would prove beneficial to have a flag against an item card (possibly within the planning section) that allows you to select whether an items stock level should be considered against its lots. “MRP to consider Qty in Lots”

This flag would then cause the MRP calculations to look at the lot quantities rather than the overall stock quantity.

An example senario;

A job requires 2.5m of aluminium flat bar. A supplier will only provide a 3m length of material (stored as 3000mm). We therefore buy the 3m length and cut it down on site, leaving us a 2.5m length for the job and a 500mm offcut of that product. If we were then to do this 5 times, the system would show as having 2500mm in stock stopping MRP from suggesting the purchase of additional material. If the item could be flagged as proposed and we had two jobs one for 500mm of material and the other for 2.5m of material, A suggestion would be made to purchase the 3m length to fulfil the larger job and the offcut would be consumed to fulfil the smaller job.

This would also work if a new job was raised that required 501mm of material. As the 500mm offcuts would not be large enough to fulfil the requirement.