The left booster "originally launched on July 18, 2016 in support of the CRS-9 mission, and landed back at LZ-1". The right booster "originally launched on May 27, 2016 in support of the Thaicom 8 mission. Notably, it earned the nickname "Leaning Tower of Thaicom"; having developed a significant lean upon a hard first landing."

Source:

https://www.reddit.com/r/spacex/comments/7vg63x/rspacex_falc... linking to details of:

- https://www.reddit.com/r/spacex/wiki/cores#wiki_b1025 - left booster

- https://www.reddit.com/r/spacex/wiki/cores#wiki_b1023 - right booster