AC III Season Pass DLC Discount

I bought an ACIII Season Pass card. It says you get 25% off all DLC. Does this bonus discount last permanently? And will it work in the future if there is a sale on DLC items? Basically.. can I stack discounts?

No what it gives you is the DLC already out for ACIII and future ones. You dont pay anything else. The 25% off thing is that is what you are saving with buying the Season Pass over getting them individually.