I didn't forget, but the second number is the potential. Haruto was born maxed out, so unless they change the concept entirely, he has no room to grow stronger with training. He can get more creative with his power, but the raw strength of his magic is set.
That is, except for a radical nature change, like humans becoming majin or something similar.
Also, we had a look at his stats since then. The last three digits at least: it would be pretty strange if he grew up in exact multiples of one thousand, but I'll grant you that this kind of contrivance can occur. He has been at 002/002 since birth, and the goddess said that his power is 1002, which is the minimal number for x002 that is not just 2.
Also, from birth, he was already far stronger than one of the former main subordinate to the previous demon lord. So Frey should place pretty high in the rankings too. I keep thinking that the number displayed for the majin girl was either wrong (should have been 3/6, or some error display if the author wanted to keep it under wraps but actually figures in the hundreds.) If she's really in the thousands, the whole setup becomes broken, either in her power level, or Haruto's... and by extension the whole concept of "max potential". If the author breaks their own setup, even more so if they did by mistake, I'll feel pretty annoyed. Nothing spoils a story for me as much as a broken setup.