Hi,
According to me for the materials which you are checking in MD04 schedule lines/Pur req exists beyond the period you defined in 'Planning Calendar'. Try to maintain 'Planning Calendar' periods for next 3-4 years means for example up to 2017 or 2018.
Also check the validity period defined for 'Factory calendar' maintained for this plant, it should valid for next 3-4 years as well.
After that check MD04 for that material.
Regards,