Glock 17C came with 2 mags. Box was marked the same. I believe this is actually a Gen 3 gun, not for sure. Manuf. date was 3-2012. I was hoping it came with three as well.
You have a Gen 3. I'm fairly certain they haven't released any Gen 4 "C" models and I know they've stated in the past that there are no plans to do so.
Gen 4 Glocks say "Gen 4" on the box. Gen 3 Glocks don't say anything on the box in regards to which generation they are.