There's no problem with merging lots of profiles into one, e.g. B into A, C into A, D into A, etc. That's fine. You could merge hundreds into A.
As Jillaine says, the problem is with chained merges. A into B, B into C, C into D, etc.
I think that what's being suggested with these unknowns is that after merging a bunch of unknowns together, then the unknowns would be merged together into one. That would be a massive, ugly chained merge. I haven't looked at the unknowns project in a while. I hope nothing is being done there that is causing trouble.