Thank you! I'd never have found it, because Scott provides only one image for that series and it's an image of the 3c, which has a very different design. The image of Mt. Momotombo is the same, but everything else--the frame, the tablets, everything—is different. And there's no mention of that fact. Scott could've done better here. Anyway, thanks again.
So in this case I've been unfair to Scott. I understood codehappy's post to mean that my stationary replicated the design of the 5c blue from the 1899 series (Scott 125). I therefore criticized Scott for not mentioning that the designs of that series differ from the sample image (A14). In fact, they don't differ at all, and my postal stationary version of the 5c is an altogether different design. And, as billsey says, Scott doesn't include postal stationary. My inference was wrong and, to make matters worse, I even own a copy of Scott 125. If I'd taken the time to look, I'd've seen that the designs don't differ, though without codehappy I still wouldn't have known that mine was postal stationary related to that series. So, despite my embarrassment, it was worthwhile posting my question.