From what I understand, the SRO line is one and the same with the Cancellation line. I.e, they sell SRO only to the people in the cancellation line. I'm assuming - though I don't know for sure - that you can pass up full priced tickets if you want to hold out for the SRO. I believe people usually start lining up before the lottery, but not too long before - maybe only an hour or two. Though it might have gotten worse.
And it seems as though most shows have been selling out, if not all.