A zip-top bag means a bag that can be sealed. There was NEVER a regulation saying it has to be the kind of bag with a plastic slider at the top.
It just has to seal. You know, like the original bags of that kind, that have a little lip on each side of the bag, and you use your thumb and finger to squeeze them together so they form a seal and you move your thumb/finger on down the line to seal up the bag.
A fold-over plastic sandwich bag would be an example of a bag you CAN'T use.