Girls Generation was famous for being the first to debut with such a large-member lineup. However, they weren't always the same nine girls we know and love today. In fact, they had a very different member idea back in 2007. So, let's talk about what they, as members, used to be like.
#1: Showcase 1:
From left to right, top to bottom, we have Lee Younghee, Hwang Bora, Bae Seokbin, Zhang Liyin,
Jessica Jung, Hyoyeon Kim, Kwon Yuri, Choi Sooyoung, Im Yoona, Seo Joohyun, Kim Yejin. The leader would have been Lee Yeonghee, and the maknae would have been Kim Yejin.
From left to right, the members are
Seohyun, Yuri, Bora, Seokbin (?), Yejin (?),
Sooyoung, Liyin,
Hyoyeon, Jessica
After this, SNSD made it's first member revision; Only the six highlighted names above made it on to be the Girls Generation that we know and love today.
This doesn't mean that the other five members dropped off the grid - Lee Yeonhee acted in the movie 'Millionaire First love', drama 'East of Eden', and starred with current member Sooyoung in 'Hello! Schoolgirl'. Hwang Bora starred in the movie 'Jumunjin' alongside Super Junior's Kim Kibum. The other members stayed in the music biz, Zhang Liyin debutted as a solo singer in 2006. Kim Yejin starred in SHINee's "Amigo" MV. All of the members, except Hwang Bora, are still under SM Ent.
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#2: Showcase 2:

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First Row: Seo Hyunjin, Park Soyeon, Jessica Jung, Kim Hyoyeon, Kwon Yuri
Second Row: Choi Sooyoung, Stella Kim, Im Yoona, Jang Hajin, Seo Joohyun, Lee Hwanghee.
These new members had big plans for SNSD - Park Soyeon was supposed to be the main singer, while Stella Kim was supposed to be the "face" of the group, alongside Yoona. However, the oldest Seo Hyunjin and Lee Hwanghee were replaced with the "new" trainees, our beloved Taeyeon and Tiffany!
Surprising Fact; Any Queen out there will recognize "Park Soyeon", with good reason - that is indeed our Soyeon! More on this later...
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#3: Showcase 3:
First Row: Park Soyeon, Kim Taeyeon, Jessica Jung, Tiffany Hwang, Kim Hyoyeon, Kwon Yuri
Second Row: Choi Sooyoung, Stella Kim, Im Yoona, Jang Hajin, Seo Joohyun.
This was the most famous lineup of the girls so far. They took an official picture that was made by SM and released. At first, they were known as Super Junior's female counterpart, dubbed as 'Super Girls'.
First Row; L-R: Tiffany, Soyeon, Hajin, Taeyeon, Hyoyeon, Sooyoung.
Second Row; L-R: Yuri, Yoona, Stella, Jessica, Juhyun
Obviously, SM was making things official. The original plan went along the lines of:
Leader: Soyeon.
Vocalists: Soyeon, Taeyeon, Jessica, Stephanie, Stella, and Juhyun.
Dancers: Hyoyeon, Yuri, Sooyoung, and Yoona.
Visual: Jessica, Stella, Yoona, and Hajin
Makenae: Seo Joohyun
Despite the fact that this was the original group that was set to be debutted, SM decided to add and cut more members. Because of their attention, lots of rumours went flying as to why Stella and Hajin were cut. There were rumours that they were cut for lack of dancing skills. For Stella specifically, it was said her parents refused to let her debut before she obtained a college degree. But both Stella and Hajin stated that they quit the group to focus on education. Stella now goes to NYU, and Hajin goes to the prestigeous KAIST.
Note: In 2011, Jang Hajin released a book labeled “소원을 말해 봐 (Tell Me Your Wish)”. The book was about her first impressions and relationships with the SNSD members. It also included information about trainee life. While Hajin said good things about all the members, she says that she doesn't stay in touch with them.
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#4: Showcase 4:
First Row; Park Soyeon, Kim Taeyeon, Jessica Jung, Sunny Lee, Tiffany Hwang, Kim Hyoyeon
Second Row: Kwon Yuri, Choi Sooyoung, Im Yoona, Seo Joohyun, Lee Hwanhee, Ha Chanmi
This new member lineup added Sunny, Lee Hwanhee, and Heo Chanmi. Sunny, despite her uncle being a high-up in SM, was recruited after a few word from Ahyoomi/Iconiq. Sunny trained in Wheesung's company, set to debut in a smaller group. But under difficult circumstances, the company went bankrupt. Sunny only trained for 2 months under SM.
Shortly before SNSD's official debut, Soyeon, Lee Hwanhee, and Heo Chanmi left the group. Little is known about Lee Hwanhee's reasoning, but Soyeon and Chanmi's explanations are well-known.
Soyeon told the media "Back then, it was tiring. And I went through much hardship. Even now, I'm still in contact with the SNSD members. I'm really happy that SNSD is doing well. Going forward I will try my best as a member of T-Ara. Although we'll be in competition with SNSD, I would like it to be a friendly competition between us."
Chanmi, on the other hand, gave a different opinon. "I was a trainee for a long time. I had participated in the recording for SNSD’s title track, and even completed the photoshoot. Since I was young, I was upset at not being able to debut with them. However, I was understanding because I knew that it hadn’t been that long since I started training. I supported the SNSD unnis and hoped for the best.”
Soyeon debutted in 2009 into CCM's girl-group T-Ara, who is similarily soon to become a nine-member group as well. Chanmi debutted into CCM's co-ed group, "Co-ed School". She also debutted into the sub-group '5dolls' in 2011.
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#5: Final Showcase 5:
L-R: Taeyeon, Jessica, Sunny, Tiffany, Hyoyeon, Yuri, Sooyoung, Yuri, Seohyun.
It's very clear who made it into the final cut. However, the nine girls debuttted into "소녀시대 ', literally translated into "The Era of Maidens". The members themselves were also bewildered by the old-fashioned name as well. They have the english "Girls Generation" name instead. And only two years after their debut, they would become the leading girl group in K-pop.