Looks like S/m 2nd gen joined in 2011, and their first appearance was on the 7th single "Tachiagirl" but as "sub-members." They were full members by the 8th single.
Posted Yesterday, 21 Jan, 08:29PM
I honestly can't remember how many or when S/mileage debuted 2nd gen... Was it after their debut?
My guess is that Tsubaki's n00bs will be called 2nd Gen, with the idea that anyone who was a member at their major debut is 1st gen, and anything that happened pre-major debut was just tweaking.
It was after their debut. IIRC, the audition for the 2nd gen was announced to everyone (including the girls) at the celebration of their 1st anniversary since debuting. I always thought it was a dick move.