Susanna, the problem is that this category with this naming does not fit into the approved system of migration categories. So you need to change something at it. I worked with the German part of that category now for a few weeks, and from what I see, the category could look like "(whatever South Africa Project decides), Immigrants from Holy Roman Empire". Seeing the German part of the category that would fit.
When you decided how the South Africa Project wants to organize its migration categories, I can send you a link to a very helpful Space Page that shows in a few steps how to rename a category. Feel free to send me a message about it.