If the box had mentioned anything at all about "magnum" it would have been a no brainer. And who makes a magnum round without a non-magnum ancestor anyway?

Lyman may have done it because the S&W .41 magnums barrels were only marked "Smith and Wesson" on one side and ".41 magnum" on the other. Marking their boxes with "Remington" would have only added to confusion since you won't find any Remingtons in .41 Magnum. Although a 788 carbine in .41 Remington Magnum would be a real gem.

And if no other manufacturers were making a .41 magnum at the time, marking the dies .41 S&W would have been understandable. The only other choice would have been the .41 Colt.