Lightsum has three from Produce48, Choron, Yujeong and Nayoung.
However, all three have very different images, and they were NOT friends back then; they were not even from the same companies.
Elsewhere I said lightsum is a hastily launched group to bury the mess Seo Soojin of Gidle created, and since Cube's emphasis is on Gidle, lightsum will be hard to avoid CLC's fate.
I do not know how long each member trained at Cube. When Gidle debuted Choron and one other trainee were training, so all of the rest joined cube after Gidle had debuted.
A good example of such kind of act is GFriend, which WAS the real last-chance group, with two faces which would not have been able to debut anywhere else (Yuju and Umji. The truth is harsh - Umji's face was the most 'interesting' of all KPop acts back in 2015, although Yuju has surpassed that now.)
The average length of training was one year and change (not counting the years the members trained elsewhere), and although Sowon was nominally the leader, all power resided in SinB.
So, when Eunha, who knew SinB for a long time, was added to GFriend with a recommendation by HItman Bang himself, SinB accepted her old friend but others were not too happy about someone who did not share the days of suffering while training under a tiny company with small budget.
The lift between Yuju, who sacrificed the most for the group, and Eunha, who basically took all the glory, was never healed and Yuju has been sidelined since late 2018 and will probably not be re-signed when the contract renews. The group turned into an act of Eunha, by Eunha and for Eunha, other members playing second fiddle to her (and those unwilling to do so cast out).
The anger of Choron, Nayoung and Yujeong, especially Choron, would be enormous and if a member who joined later gets promoted heavily the anger will not be controllable. Since Cube has a long history of backing the wrong member, it is pretty likely that a newcomer (most likely Sangah and Hina) would be the front person and the three PD48 contestants, who are NOT friends btw, won't tolerate that.
I personally think Lightsum will be better known with the drama it would create rather than its songs.
