I think the difference is that unlike the Pacifista where Kuma was the original and the others were modified machines to be "like" Kuma, the Serephim seem to actually be individual lunarian children.
Look at where King was when Kaido rescued him. Plus, all of the Serephim allegedly are unique in design and not the same. I think it suggests they are all actually Lunarian with their own powers, plus the augments that the SSG gave them, potentially.
I wouldn't consider these just nameless copies is what I mean.