Rerolling stats

When it mentions re-rolling stats, it says the following currently: "You can also reroll the current grades stats with an Echostone Supplement". To clarify, does that mean if you wanted to max out your benefit you'd have to re-roll the current bonus every time you advanced in order to maximize your stone? Or does it actually mean that you could re-roll at any advancement level and be anywhere within the minimum and maximum possible benefit? IE: If I were to re-roll at advancement 23 in the chart, would I be able to get a stat bonus between 23 and 74 or would I only be able to modify my current stat bonus value by the 1-7 gain I got from the last advancement?

Annoyingly, every Grade 1-24 needs to be rerolled (while on that current grade). I made this a little clearer on the Echostone Supplement page but it feels so archaic of a system that I'm not confident on it. It's really just a method to provide perfect Echostones if you're intending on running a lot (a lot) of the dungeon.

Thanks for clarifying! Will have to keep track of my rank ups and see how much time I'm willing to spend I guess