What choc said plus our experience may be helpful...
DS has a social communication disorder or delay (but he ain't catching up so I think it's fair to say we're dropping the delay) but he is not on the autistic spectrum.
When children go through ADOS, they are observed and scored for various 'markers'. If they score sufficiently high enough on enough of these markers it is an ASD dx. If they don't, but score higher than an NT child would, that's where you start to hear HCPS talking about 'autistic traits' - i.e. they aren't NT, there are areas of concern, but they aren't 'autistic enough' to get an ASD dx.
For DS, those areas of concern were all around the social/communication area, so that became his DX.
Now, I always read dolfrog's posts with interest because he is so specific about the various co-conditions that exist. In my healthcare area, there seemed to be no interest in getting a more specific dx. For example, if someone posts on here about APD or dyspraxia and I follow a link and think 'that sounds familiar', but no-one seemed to be interested in pushing for a more specific dx.
I often think about going back and pushing for another shot on the dx roundabout, but as DS is doing well at the moment and we are getting support I'm probably not going to. But I reserve the right to change my mind on that!
So. SCD is not ASD, SCD is a condition in its own right which does not mean you may go onto get an ASD dx. But there may be other conditions which SCD dx is, in effect, covering up. But for me, how specific I need to get with dxs is really about how much I need a specific dx to get support.
Sorry LONG! 