Hmm. I had grepped the source for Serial and saw these lines:
TTYUARTClass Serial(&rx_buffer1, 0); // ttyS0
TTYUARTClass Serial1(&rx_buffer2, 1); // ttyGS0
TTYUARTClass Serial2(&rx_buffer3, 2); // ttyS1
so I assumed that these comments were meaningful. Sorry if that is not the case.