How do you get to stack all these discounts?
I think coins should always stack with discount codes (the $35 codes work now as well), and the other two aren't discounts in the typical sense: The seller's adjustment is just that and applied after placing the unpaid order and messaging them about a discount.
The final price adjustment is due to the order exceeding the EU limit of custom/tariff excemption and VAT pre-collection via AliExpress, so VAT is removed from the order but will/might have to be paid upon or before delivery, as well as custom duties.