You would be correct. There's nothing written in stone that says a split pattern is best for manifolds and single pattern best for headers. That's an unknown that cannot be known until you hit the street, drag strip or dyno. And yes, it's splittin hairs. I wouldn't sweat it a bit.
Dual pattern usually have more duration on the exhaust to compensate for a restrictive exhaust, whether from port design or the manifolds. Frequently have less lift as that is not a big problem on the exhaust.
With good exhaust ports and headers a single pattern tends to provide a bit more low speed to mid range torque.
You are correct Rusty, kind of splitting hairs.