I hadn't thought of a rolling spawn. In those cases, I think that can give the appearance of multiple spawns when they may or may not occur. I've often wondered whether the last spawn had the success rate of the first. I wouldn't think so but have never seen documentation.

I know more than one spawn sometimes happens in warmer climes. Although not really noteworthy, I think these are more the exception than the rule. In my mind, that doesn't qualify a seller to make a blanket statement.