Good question that I don't have an answer to.
Those were taken on different days and probably with different lots of ammo as well.
The 2506 is a 10-shot average, SD 25.4, ES 73, 55*F, 90% humidity, 30.17" Hg.
The 2583 is also a 10-shot average, SD 12.9, ES 44, 86*, 49% humidity...