Both are wild species and are related so a form of one could look like a form of another. Look in a rhododendron book that give technical details to see how to check identification to species level at least. If raised from seed taken from a cultivated specimen one (or both) could also be a hybrid. And a labeling mixup could certainly be possible as well.

Hi albertine, I don't know about R. fortuni, but R. decorum ssp. decorum's flowers are tinged yellowish right at the base. It looks like a light at the end of a tunnel. I love the species rhodies too.
-Au

Here is a link that might be useful:

I'm not too familiar with R. decorum, but R. fortunei tend to have purple petioles.

R