FYI I have bought Hitman GOTY Legacy pack on steam, but it activated as "the complete first season" which does not include any of the GOTY content. As seen in this post, other users who have bought Hitman GOTY Legacy pack dlc from cdkeys also experienced similar problem.
Funny enough there is a non-goty, more expensive entry on cdkeys. I wonder if that one is mislabeled and is actually the goty version of the DLC.