all the 1999-2000 packs ive seen come in packs like that, but only way to tell is to open it. Its also more likely to be 1999-2000 if it has a ‘distributed by hasbro’ sticker on the back from my experience
EDIT: on topic though, there IS an actual pack error though. A small batch of unlimited boosters were accidentaly stamped with a 1st edition stamp, meaning that a ‘1st edition’ pack had unlimited cards in. They caught most of the errors and covered the stamp on the pack with a black triangle, however Ive been told you can still get the packs without triangles (though they are incredibly hard to find, any truth to this?) they dont hold that much extra value though (the triangle packs at least)