The number for 50-55 is incorrect. 50-55 is 6,616,800 exp total.
The 2-level step numbers are correct(when adding 50-52 + 52-54 + 55s XP you get 6,616,800, same if you add each individually) and the 55-60 number is also correct.
Otherwise an extremely useful resource that I have been using for A VERY LONG TIME. Thank you very much, Dominique.