I would assume that what you might think is a better wood might just be a better quality Luan on the inner ply- I don`t think we`ll ever know without some kind of chemical analysis.
I'm not a carpenter or woodworker, but the wood looks fundamentally different to me. The grain pattern of the mystery wood is much tighter and clearer (right), when compared to the drum which is obviously luan (left).
I've had Pearls with hardwood rerings, and I remember seeing someone posting a Champion snare that definitely didn't look like luan either (with what looks like a luan reinforcement piece).
I've heard it suggested on this site that late-period Rogers were manufactured by Yamaha using birch shells (can't really see the wood grain, but that shell looks very similar to the Rogers R-360 bass drum I have, with the same gray interior).
Seems totally possible to me that there were MIJ drums that weren't luan from that period, especially if it's from the late 60's or early 70's, when Yamaha began making drums.