I had that concern when I did my BBG a few years ago. I planned my route as a double out-and-back. I'll explain a little further.
Since I live in the quad cities in IA (point A), I found that a round trip to Mitchell, SD (point B) and back gave me a SaddleSore route. I then found a route with a turnaround about 250 miles out, in my case, Crawfordsville, IN (point C). So after returning from SD, I could bail at home and still net a SS1K, or (as I did) continue with my plan and bag my BBG1500. So my route went like this: Point A - Point B - Point A - Point C - Point A. I didn't really stop back at the house in the middle, but when I went by, the sun was still up and I knew that I was in good shape. It was quite the security blanket, and I didn't have to spend money on a hotel.
Since the rides of the Southern California Motorcycle Association are their rides, I would tend to believe that they do NOT count toward IBA Mile Eater awards...unless you combined an IBA ride with SCMA's ride (e.g. submit BB1500 or SS1000 as part of the SCMA ride)
Ira will be by and provide us the definitive response on the subject.