I think the intent of using “originally designed” is so that it doesn't capture the aftermarket magazine. There could be firearms that were not originally designed with a certain magazine, but then there could be a magazine that comes out in future years that also fits that firearm or that is made for that firearm. The word “originally” is so that you don't start capturing those aftermarket magazines.
On May 2nd, 2023. See this statement in context.