I didnt have the boxes, but it does say on the back of them.
J939 (black)- bootrom success Downgrade success
J945 (black)-bootrom success Downgrade sucesss
J949 (plum)-bootrom success (did not attempt downgrade, on 220.127.116.11)
Mine has J035 (black).
These look a lot, like they could be year and week of production.
I.E J939 being 39th week of 2019.
J035 being 35th week of 2020 etc.