This is unlikely to ever come up practically speaking, but I'm almost positive that it's implemented incorrectly. In Gen 2, Special Defense and Special Attack are only differentiated by the base stat, everything else used to calculate the stat is identical for the two. While the sim does have this for making sure the Special Attack and Special Defense DV must be identical, this is actually also true for stat exp as well. There's no such thing as "SpDef Stat Exp", only special stat exp (determined by opponent's base special attack ingame).
On the sim it's currently possible to set the EV slider for Special Defense to a value different than that of Special Attack and vice versa, as well as use it in a battle. Since special attack and special defense have to share stat exp this shouldn't be possible.