I've come across a post from sosiz in Korea that telling how SNSD are formed back from  the beginning of their training day till now. And how is the original plan of SMent for the Girls and who were the original members from the group..so on. The above picture is the road history selection of Girls' Generation.
Below are the  translations for the picture content;


Initial group members


 2005~2006
SM New Girl Group Showcase
In 2005, SM Entertainment debuted a large boy group Super Junior, and then proceeded to plan a similar large girl group counterpart. SM put together a showcase comprised of internal trainees; most were veteran trainees and the total number of girls featured was 11.

(Clockwise from top left: Lee Yeon Hee, Hong Bo Ra, Bae Seok Min, Zhang Li Yin, Jessica Jung, Kim Ye Jin, Seo Ju Hyun, Im Yoon Ah, Choi Soo Young, Kwon Yu Ri, Kim Hyo Yeon)

Notes:

Currently an actress: Lee Yeon Hee
Zhang Li Yin is currently a solo singer with SM Entertainment.
Jessica Jung was a Korean American Trainee.
Leader: Lee Yeon Hee (born in 1988)
Maknae: Kim Ye Jin (born in 1993; only in grade 3 when she joined the company).

// So initial there are 11 members from them, the SNSD members nowadays only have Yuri, Sooyoung, Hyoyeon,Yoona,Seohyun,and Jessica were in the line-up plan. Seem like they've pretty much secured of their place from the beginning. ~^_^~ Interesting~~~


SM Girl Group Project Revision 1
IN: Seo Hyun Jin, Park So Yeon, Stella Kim, Jang Ha Jin, Lee Hwan Hee
OUT: Lee Yeon Hee, Hong Bo Ra, Bae Seok Min, Zhang Li Yin, Kim Ye Jin

(Clockwise from top left: Seo Hyun Jin, Park So Yeon, Jessica Jun, Kim Hyo Yeon, Kwon Yu Ri, Lee Hwan Hee, Seo Ju Hyun, Jang Ha Jin, Im Yoon Ah, Stella Kim, Choi Soo Young)

Notes:

Seo Hyun Jin was a member and a lead vocal of a four-girl group called M.I.L.K.
Interestingly, the provisional name of this early group was "Seo Hyun Jin Group".
Stella Kim was a Korean American Trainee.
Park So Yeon is currently a member of the girl group T'ara.
Leader: Seo Hyun Jin (born in 1985)
Maknae: Seo Ju Hyun and Lee Hwan Hee (both born in 1991)

//Lee Yeon-hee, she is well known as an actress and model under SM Entertainment. She made her first appearance in Moon Heejun's MV, "ALONE" in 2001 and officially debuted in the Korean television drama, Sea God as young Junghwa in 2004. In 2007, soon after the debut of labelmates Girls' Generation, she revealed that if she had not decided to continue her career as an actress, she would've become a member of Girls' Generation, as they have trained together when they were still trainees.
I'm sure who sure have watched the Korean movie ' millionaire first love' would know about her, she's quite talented in acting and popular as actress in Korea.

 SM Girl Group Project Revision 2
IN: Kim Tae Yeon, Stephanie Hwang
OUT: Seo Hyun Jin, Lee Hwan Hee



(Clockwise from top left: Park So Yeon, Kim Tae Yeon, Jessica Jung, Stephanie Hwang, Kim Hyo Yeon, Kwon Yu Ri, Seo Ju Hyun, Jang Ha Jin, Im Yoon Ah, Stella Kim, Choi Soo Young)

With Seo Hyun Jin and Lee out of the running, SM invited a regional trainee Kim Tae Yeon and American Stephanie Hwang (who at the time had only trained for 2 years). SM initially planned to stick to these 11 girls and actually took some still cuts/pics of them.
This line-up is probably the most well-known line-up for the so-called female counterpart of Super Junior. At this point, netizens started calling this project group as Super Girls. In fact, SM Entertainment initially planned to debut this 11-member girl group. They even already took group picture of them.




Initial roster:
Vocal Line: Park So Yeon, Kim Tae Yeon, Jessica Jung, Stephanie Hwang, Seo Ju Hyun, Stella Kim
Dance Line: Kim Hyo Yeon, Kwon Yu Ri, Choi Soo Young, Im Yoon Ah
Visual Line: Jessica Jung, Stella Kim, Im Yoon Ah, Jang Ha Jin

Notes:

Stephanie Hwang was a Korean American Trainee.
Leader: Park So Yeon (Born 1987)
Maknae: Seo Ju Hyun (Born 1991)

SM Girl Group Project Revision 3
IN: Lee Soon Kyu, Lee Hwan Hee, Heo Chan Mi
OUT: Stella Kim, Jang Ha Jin

(Clockwise from top left: Park So Yeon, Kim Tae Yeon, Jessica Jung, Lee Soon Kyu, Stephanie Hwang, Kim Hyo Yeon, Heo Chan Mi, Lee Hwan Hee, Seo Ju Hyun, Im Yoon Ah, Choi Soo Young, Kwon Yu Ri)

SM initially planned to debut with the 11 girls from revision 2. However, Lee Soon Kyu was recruited as an additional trainee thanks to rave recommendation from SM singer Ayumi, and added another trainee named Heo Chan Mi. They re-recruited Lee Hwan Hee as well. During this process, Stella Kim, once highly touted prospect of SM, was cut mainly due to her lack of dancing skills.

From top left ~  Hwanhee, Hyoyeon, Taeyeon, Jessica, Soyeon, Chanmi /
Second Row  Left~ Juhyun, Soonkyu(Sunny), Yoona, Yuri, Sooyoung

Notes:

Lee Soon Kyu was originally a trainee with another company; she transferred over to SM after an audition.
Leader: Park So Yeon (born 1987)
Maknae: Heo Chan Mi (born 1992)


 SM Girl Group Project Final Confirmed Roster
OUT: Park So Yeon, Lee Hwan Hee, Heo Chan Mi

(The current group; I'm sure you guys know who's who)

After numerous revisions, the remaining trainees were put through what was ultimately a final audition process; SM had decided to cut the number of girls in the group from 12 to 9. The final audition resulted in Park So Yeon, Lee Hwan Hee, and Heo Chan Mi being cut, resulting in the current 9 members.

The 9 remaining girls were then officially named "So Nyuh Shi Dae" and took official profile pictures.



Chronicles of their initial debut:

July 6, 2007: Teaser of the first confirmed member, YoonA, is released
July 7, 2007: Teaser of the second confirmed member, Tiffany (real name: Stephanie Hwang) is released.
July 8, 2007: Teaser of the third confirmed member, Yuri, is released.
July 9, 2007: Teaser of the fourth confirmed member, Hyoyeon, is released.
July 10, 2007: Teaser of the fifth confirmed member, Sooyoung, is released.
July 11, 2007: Teaser of the sixth confirmed member, Seohyun (real name: Seo Ju Hyun) is released.
July 12, 2007: Teaser of the seventh confirmed member, Taeyeon, is released.
July 13, 2007: Teaser of the eighth confirmed member, Jessica, is released.
July 14, 2007: Teaser of the final confirmed member, Sunny (real name: Lee Soon Kyu) is released.
July 16, 2007: Group footage and the name "So Nyuh Shi Dae/Girls' Generation" is released.
August 3, 2007: The debut album "Da Shi Man Nan Sae Gae/Into the New World" is released.
August 5: 2007: The girls make their first public TV performance in SBS "Inkigayo".







 They've really come a long way to form this  group 'Girls' Generation'. I'm really glad able  to know more about them. Nine girls who have been  working really hard to be on stage and fulfilling their dream. Nine girls with so different in personality and each other, working together to chase the same dream and finally have become one.
The Power of 9 ~~~~~~~~~~~~~
They really deserve love from all the fans and happy I'm one of them ~^__^~.






nicholas@NOW Is Girls' Generation
Source & pictures:sosiz, soompi,Daum
thanks to ahjussi fo soshified for the translation part