Perhaps this isn't very uncommon, but it seems strange to me nonetheless. I was looking at one of my SNES controllers the other day, and I noticed that on the back it says "super famicom" and it has the super famicom logo. In fact, it doesn't have the SNES logo anywhere on it, even though the buttons are purple unlike the Japanese ones. Moreover, my other SNES controller simply says "Super NES Controller" on the back and has the SNES logo on the front. The weird one just has a nintendo logo here. I'm positive that this controller is American, so why does it say "super famicom?"
they probably used some japanese shells because of a production shortage for the american ones in the early days. nothing more than a guess, though.
I have a few US SNES controllers with Super Famicom on the back. One is with a console in box (deff not a early model BUT console is mint where as controllers are not so could be different controllers to the console) The other two were picked up loose in a big US SNES bundle I purchased a couple of years back. I had always guessed that they were early models, but never really spent much time looking into it.
I have two of these controllers as well. They are from the last batch of SNES/SFC controllers produced. I believe the reason they were produced this way is so that Nintendo could consolidate the design to accomodate all regions. All Nintendo would have to do is put in the appropriate AXYB faceplate for whichever region and the matching colored buttons, and presto -- savings in the bank and controllers for everyone.
Even with the last run controllers, they stopped using the Purple buttons, confused the hell out of me when I was little and I thought they were fake.