The extra hole is for a seperate taper crimp die. Actually, the small hole in your other tool heads is also for a taper crimp die. The tool heads with the small hole are older, and Star made a special taper crimp die that was inserted in that hole. Later they switched to a hole drilled and tapped for the dies the same size as the sizing and bullet seating dies.
For rimless auto cartridges, the most accepted practice is to give them a taper crimp rather than a role crimp because the bullet indexes on the carse mouth. This is best done in a seperate station rather than in the bullet seating station. Some people prefer to use a taper crimp die for rimed cartridges as well. It sounds like you have a relatively rare taper crimp die for 38 Special.