prod. order starting date and capacity issue

Here I am confused by an issue about starting date in production order and capacity load in our live database navision 3.01B. I notice that starting date of some production order is far more early, which is in Y2003. however its due date is March Y2005. But I check its work center load in last and next months and find it load is less than 100%. BTW, the efficiency of the work center is setup as 100%. Do you have any ideas about it? Why some starting date is so early? In my opinion, since the work center is not under full workload, the production order should be scheduled in current month and last month?