You're supposed to engrave the city and state of where the firearm was made. As in where you're physically located at the moment your have an SBR. It may have nothing to do with your home or work location.

If you left 4h blank on the F1, you simply engrave the location you make the firearm. If you put your old city, state in 4h...you technically have to engrave that plus where it's made. Or go back to that location to make it.