A correctly converted particular affirmative or universal negative can be converted once more to recover its original form.
“Some students are memorizers.”
First converse: “Some memorizers are students.”
Second converse: “Some students are memorizers.”
Likewise:
“No tree is a stone.”
Converse: “No stone is a tree.”
But converting a universal affirmative first reduces it to a particular, and converting that back does not recover universality. Conversion may therefore lose information about quantity.