Official calendar year production numbers from Karmann:

2003 Coupe: 18,470 - Roadster: 19 - Total 2003 = 18,489
2004 Coupe: 19,426 - Roadster: 16,250 - Total 2004 = 35,676
2005 Coupe: 4,126 - Roadster: 8,329 - Total 2005 = 12,455
Total Coupe: 42,022 - Roadster: 24,598 - Grand Total = 66,620

The VIN appear to be sequential. The VIN on my car is 54018 with a manufacturing date of 12/2004. According to Karmann a total of 54,165 had been built from 2003 to the end of 2004.