I believe it was the Iguana Tweaks mod that allowed this,
Basically
if an stone pick is on level 1 (freshy crafted) and it leveled to level 2 its mining level would now be iron now. it would stay iron on level 3,4,5,6... etc. just the first level up increases the level!

I absolutely loved this feature in Iguana tweaks and would love to see this ported! it was soooooo amazing for progression!

Not in the scope of TTL. I've deliberately kept the scope of this mod to purely leveling and adding free modifiers.