Special subvarieties are absolutely special

Let $S$ be the base of the family considered in the paper. A special subvariety is a closed irreducible complex subvariety maximal among those having a fixed generic Mumford–Tate group; an absolutely special subvariety is defined analogously using the generic absolute Mumford–Tate group. Special-to-absolute-special conjecture. Any special subvariety is absolutely special.

The source explains that absolutely special subvarieties are already special and $\ell$-Galois special, and conjectures that all three notions coincide. No resolution is supplied for this implication.