Nonsense! If I look at the Atlantic now, without any filters, I can see virtual flocks across the centre of the Atlantic. EG; Norwegian DI7043 approx half way between Gatwick & Miami and BA027 from LHR to MIA. While the tracks in those positions may not be ADS-B plots, they are extrapolated from flights that were being plotted on either side of the Atlantic until they went out of range of ground based ADS-B receivers. The tracks are usually not too far off the mark.