It would be my guess your question happened early on in the war but then again after various calls for more troops could be possible.I have seen this happen because of quotas. Say Lincolns first call for 75,000 men.I know more about IL. regiments.In general each state functioned simularity. Certain Counties might of reached their qouta with many men still wanting to muster. Not wanting to wait you could travel to a county still excepting men. This is what happened in my GGGrandfathers regiment,Company K., as several men,brothers, were from across the state Approx.200 mi..All mustered in Aug. of 1861 These men boarded a train the qouta at Quincy filled and traveled to Aurora still excepting men.

I have also seen this because of Bounties paid. In the fall of 1862 some counties and cities paid bounties to those mustering in some cases as much as $200.00 but, usually around $50.00. A tidy sum by nineteenth century standards and worth the price of travel.

Good luck!