Why There are Stock Ratings in Old Articles?

Based on SA Product Team's posts, author stock ratings and Quant ratings were introduced in March 2019 and May 2019 respectively. However, I can see that these ratings were shown for dates before 2019. While I can understand that quant ratings can be computed using historical data, I cannot understand why articles in the past (even in 2015) would have author stock ratings if this feature was added in 2019. 

May I ask for clarification on this? Thank you.