Baileys, I wasn't suggesting no-one scans black tracks. I said I would understand people controlling high level class a airspace only, if they didn't. Short of posting errors and inhibited tracks, the only black tracks you would have are filtered or no mode c. And you can safety assume vfr aren't going to be in class a, so you would probably just ignore anything black after a while. This is only an assumption, different if you are controlling lower levels, and my possible explanation for other controllers missing it, as it flew through sectors.