If you are talking about the tubes only, you are correct. They are the same for 9mm and 38 super. The package is probably marked that way because there is no spacer in the package. Is that correct?
If you are talking about complete magazines then the springs and followers would be different between the two. The 9mm would be shorter to allow room for the spacers to fit in the tube. So, they would be marked different.
I have both 9mm and 38 super and I can change the springs between them. My 9mm STI runs fine with the 38 super springs and followers. So, my mags will interchange between my open gun and the 9mm gun.
I hope I am making sence.