GOT7's JB & Jr.
Both Jb and Jr. made their first appearance in the drama Dream High 2 along with 2AM's Jinwoon, SISTAR's Hyorin, T-ara's Ji-Yeon, and Ailee. They later debuted as a duo under the name JJ Project following the conclusion of the drama. JJ Project released their hit single "Bounce" in May of 2012 before joining GOT7 two years afterwards.
Hyuna was originally a member of Wonder Girls before withdrawing due to health issues. Although she withdrew, Hyuna was in Wonder Girls debut music video. She then later debuted with 4MINUTE as the main rapper and later as a duo along with BEAST's Hyunseung called TroubleMakers.
WINNER's Song Mino
Mino was a member of a ballad group called BOM. He first debuted as a rapper under the stage name of Tagoon in 2011. However, the group disbanded two years later and he was then a trainee of Stardom. Mino was initially suppose to debut with Block B but he left due to personal reasons. He was then casted to YG and later debuted in 2013 in the group WINNER.
Solji first made her debut in 2006 in the ballad duo group called 2NB. The group lasted for 6 years before disbanding in 2012. She then joined EXID that same year, the other girl (Kim Song Yi) then later joined in a girl group called Blady in March of 2015.
Was a former member of XING along with U-Kiss member Kevin. He joined XING under the stage name of "Popping Dragon" in 2007 but left in early 2008. He then debuted with BEAST in 2009.
Sooyoung initially debuted in a Japanese duo group called Route-O at the age of 12. The duo later disbanded in 2003 after releasing 3 singles. She then later joined SNSD in 2007. After debuting with SNSD, Sooyoung lost touch with the other duo member, Marina, but was able to come in contact with her through some SONEs.
Kevin, along with former U-Kiss member Kibum, were part of a group named XING. Kevin left XING in 2008 and debuted with U-Kiss later that year. XING disbanded in 2010, although unoffically due to series of line up changes and member add-ins.
BESTie's Haeryeong. Uji, and Heyeon
Haeryeong, Uji, and Heyeon were originally all part of EXID before parting due to both agency, YNB Entertainment and Shinsadong Tiger, breaking apart. The former 6 members were split in half. The 3 who stayed with YNB Ent., Hani, LE and Junghwa stayed to make EXID and while adding in Solji and Hyerin to make the 5 they are today. The other 3, Haeryeong, Uji, and Heyeon left with Shinsadong Tiger and debuted as BESTie after adding in a fourth member Dahye to the group.
G.O debuted in a group named TYKEYS in 2007. TYKEYS was a co-ed R&B group that consisted of a female singer, a male singer and a rapper. (Almost like Lucky J). After the company went bankrupt G.O went to court to get his contract nullified. He then later debuted with MBLAQ under the stage name G.O in 2009.
At the age of 12 Sohyun debuted with a girl group called "Orange". The group however disbanded later that year due to online anti-fans and cyber bullying. She later debuted as a 4Minute member in 2009.
Boys Republic's Sunwoo
Sunwoo was a former member of Touch who debuted in 2010 along with 4 other members. He then left the group early 2011 and changed his name form Dabin to Sunwoo. In 2013 he debuted with Boys Republic.
When Dara was still in the Philippines she debuted as an actor and singer. She released a 6 song album. The title song was called. "In or Out" and was sung in Tagalog. She then moved to South Korea along with her brother, MBLAQ's Thunder, and was casted to YG. Dara later debuted in 2009 along with other 2NE1 members.
Debuted in early 2009 as a solo artist under the name AJ. Hyuna who was also a CUBE trainee was featured in the mv while Yoseob and Doojun was backup dancers for Gikwang. 6 months later and he debuted with BEAST under his real name Gikwang.
4 pf the 5 members of MAP6 were former A-Prince members. Map6 just recently debuted in 2015 with their single "Storm"
All member of DGNA were former 3rd-4th generation members of XING before debuting as DGNA in 2010.
JYJ were former members of popular SM group called DBSK. DBSK was a 5 member group consisting of JYJ and TVXQ. However due to reasons, such as a slave-contract, right of payment and many others, JYJ nullified their contract and left SM. The remaining 2 the changed their name from DBSK to TVXQ. JYJ then debuted again in 2010.
Although leader of MADTOWN Moos, never debuted with MBLAQ, he did do CFs and photoshoots with MBLAQ. He was initially suppose to debut with MBLAQ but due to shoulder surgery 2 weeks prior to MBLAQ's debut he was dropped. He's stage name was suppose to be "Thunder" and the rapping that is Thunder part in MBLAQ's first album JUST BLAQ is Moos' voice because Thunder joined the group 15 days before debuting.
I hope you guys liked this card! I had a fun time trying to figure who debuted first lol If I missed anyone please let me know! And could you just imagine if the groups were still together?! That would be 대박!