I was under the impression that all the Followers of the Sufferer could do was breed a lusus of The Sufferer's blood colour, so that once his descendant survived the brooding caverns he would have a lusus to take care of him (since he would almost certainly die without one, as The Sufferer almost did). That, and they somehow gave Karkat his sign, however that process goes. Source for all that on page 005956

Hm, it looks like you’re right. Good job.

Besides, with adult trolls being banished from Alternia I guess it would be nearly impossible for a follower to retrieve Karkat.

~Mod T