Yeah I’m not sure how many have been available for pick up at sdcc, but I think there’s been a couple over the years.
There’s been a few not available at Sideshow. Three or four over the years I think. Which, out of like 600ish figures, not bad percentage really. Because there’s other lines outside of the mms stuff. The 1/4 for example, the video game line, and so on. Having them available at sdcc is not common, but them not showing up at all at sdcc is pretty rare. Some are listed right away, and others are done after other events. I think the exclusive bvs Batman was listed a couple weeks later, after both sdcc and the Hong Kong show. Not 100% sure on if it was that one or another but I recall it happening.
It would be very unlikely it didn’t show up on Sideshow and a little unusual for it (or any other toyfair branded figure) to show up at sdcc.
Edit-I think the new avengers scarlet witch was one that was teased, then showed up at Asian shows, then eventually on Sideshow. There was a lot of people freaking out about that one if memory serves me. And maybe the rose hill stark was one that wasn’t on Sideshow. And two of the early mk6 variants I think.