I suppose it could be. I get my streamer and Level II quotes both from Ameritrade. The bid/ask as shown on the streamer is always synchronized with the bid/ask on the Level II. But there could be some delays in Ameritrade receiving execution reports from the various sources, so trades that they show as executing at time T might have actually executed several minutes previously. That would explain it.

These days, when Goldman Sachs shows $100M trading profits on 3 out of 5 days, and never any days with trading losses, I tend to go with the paranoia, rather than the innocent explanation.