Muv, there are early central-bobbin model 15s (and 115s) that had a rotary hook. You'll only find this on the 15s that lack reverse, and typically with the spoked handwheels. There was actually a post in this forum somewhere about that very topic, but I cannot remember the subject line. I want to say it was started by a fellow named Joe.
In response to Jodie writing "If the original owner ordered the machine specifically with the star decal, (and I'm not saying they didn't) I have to wonder how they even knew it was an option. Information was sparse in those days, as opposed to today's internet world, and how would the buyer even know about options - but then maybe they saw a full Singer catalog or whatever."
The fact that the "SV" options even existed means there must have been some mechanism for buyers to choose "Special Variants" in the first place; I assume there was some type of catalog available at Singer stores of the era. In the early and middle parts of the 20th Century, Singer had stores worldwide that were akin to the Apple Stores of today--customers could go in, try and/or buy machines, and take sewing classes.
Also, whether a machine had reverse or not depended on both the model as well as the year. As you've pointed out, the Featherweights all had reverse from the time they debuted in the 1930s; so did the 201-2s, which came out around the same time. However, the 66s and 99s of that era lacked reverse until some time in the 1940s.
There is one other possibility for how your particular machine came about, though I admit it's a longshot. I recently started reading an excellent book called "Freedom's Forge," which is about the American industrialists tasked with revitalizing American industry for the war effort. Under their programs, a lot of American industry was diverted away from the commercial sector and instead turned towards wartime production. While it's not explicitly mentioned in this book, I'd learned elsewhere that during this era Singer produced bomb sights for bomber planes and even firearms. While we Americans didn't offically get into the war until December of 1941, I was surprised to learn in "Freedom's Forge" that industrial preparations for both "Lend-Lease" (us manufacturing materiel for the Brits) and our own military began as early as 1939. Thus, to make a long story short, it's possible that Singer's domestic sewing machine production was curtailed around the time your machine was ordered--meaning it's possible that your machine is actually a refurbished version of an earlier model 15, sent out with the unusual decals somehow diverted from Kilbowie (which presumably had bigger fish to fry in 1941).
I must say: It drives me nuts that we'll probably never learn the full story behind your machine.