Had some more super incubators laying around and decided to hatch another batch of nine 10km eggs at once. While I was saving up the 10km eggs, Niantic released the three extra egg storage and 12km eggs. So I made it a point to save three of those as well and hatch everything at once. The oldest egg was from December 16, 2020 and the most recent was April 19, 2021. Spoiler: It was all very disappointing.