There are some unexpected aspects to discount codes.
If you copy the blueprint into several children, the discounts count independently for each event so it is not tied back to the national one.
If you initially have a discount locked at the national level and all of the discounts available are used up at the child level, then you decide to unlock the discount and push it down it does not over-write the discounts which have been already used.
If the discount itself is edited at the national level (such as the name or the code itself) and then pushed down the change will go down so long as it is locked. If the discount was not locked originally and changes were made at the child level, the locking & pushing will over-write any changes that were made at the event level. It will also start the count over on the child event, acting as a new discount code.