We have some tallies from past data. Is there a way to initialize the system with past data?

Yes, there are two ways to initialize the system with past information. One way is to load the actual past schedules into the system. There is no limit on how much past data you can load. The other (simpler) method is to load summaries in the form of tallies. These summaries can then be used by the system to produce new schedules based on historical data.