Discount codes don't stack. If you have 54% off discount, they can't also use a "free shipping" coupon since Only one discount at a time can apply to a single order at the sense-u site.

Normally, one discount code is only applied for one offer. However, If the users put a vast of items in their cart, it is easy to use one coupon code to purchase items. It depends on sense-u's policy, you can contact sense-u via mail for your reference.

Usually, Coupon Stacking is not allowed at sense-u. However, the store will surely give out notice if available.

Yes. The old coupons from sense-u will be kept on the page if it has not expired. New coupons will continuously be updated.