Exactly 4 years ago on April 29. 2015 Japanese media and Hello! Project Station announced that the new group of 6 members have been formed. All those members were chosen from Hello! Pro Kenshuusei.
Next year on August 13. Tsubaki Factory became a 9nin group as 3 more girls from Hello! Pro Kenshuusei joined the group.
Here’s some kind of visual timeline of Tsubaki Factory’s years from 2015 to 2018.