Early bird discount?

I would contact the RS Travel Desk with your question just incase their web master does not see your post. Better to get an answer from the authorities rather than rely on us volunteers here.

The $100 Early Bird discount for 2016 departures was applied to tour deposits received by December 1, 2015. (Discounts have never depended on early payment of the final bill.) However, selected departures currently have even larger discounts available! See the round-up at https://www.ricksteves.com/tours/discount-tours.

If I remember correctly, I think you get some kind of discount if you pay by check rather than a credit card.