> We are using Shipworks software and we import order details from the website. When we create the shipping labels for new orders, shipworks will automatically put the order number as the reference number to the shipping label.

This is very useful - thanks for the idea.

> I just tried to search the package via reference number/order number on UPS websites and it worked. I also need to enter ship date range and zipcode info together with the order number.

Yes, the just don't have this capability from the API (although they claim to be working on it).