None of the series that CBS has already renewed are first-year series.
The only thing that has been said about the network's crop of Freshman shows came from Les Moonves, who said that the network was going to renew 5 of their 6 Freshman shows.
The decision on Supergirl's future has already been made for WEEKS at this point and conveyed to the people involved in the series, with said individuals making decisions and comments based on what they were told.
Not only has a concrete casting announcement already been made for Season 2 (Linda Carter as the U.S. Peesident), Greg, Andrew, Melissa, and Chyler have all spoken about Season 2 being a reality.