I don't know if you have different 9mm loads, but I use my nickel plated 38 special brass for a specific load. The nickel lets me differentiate them from another load that uses the same bullet. I do something similar with 12 gauge hulls. Different color AA hulls for different loads; 1oz, 1 1/8 oz, 1 1/4 oz...
I have 13 different loads for 38 special. Of course I keep them in different containers, but cases, primers, and bullets help me keep them separated when in use.
Use the nickel cases for a different load. I do not shoot 9mm as much as other handgun cartridges, but I do have 8 different loads, depending on the gun and/or use.
You can also take your calipers and measure thickness. I highly doubt you'll see much difference other than from brass brand to another. I've noticed the head of a case is slightly different from one maker to another. I bet case thickness is also slightly different.