That's a new one. So you could use all of them together if the order was big enough?
Would you care to test this by making an order?
BUT DO NOT APPLY COUPONS AND DO NOT PLACE THE ORDER - because if you do, coupons will be used even if the order expires.
I already sold and transferred them all, but I did test initially with trying to order multiple S19 ($1,897) and it let me apply a maximum of 189 coupons for each unit.