eqd stated:
It's theoretically possible that two piles of objects separated by only a few hundred meters could be in diverging current streams (especially as the North and South equatorial currents meet and diverge in that area of the Atlantic). 85 km over several days is less than 1 km/h relative difference velocity.
This seems logical to me; it is a small difference in velocities given the times involved. Unless an expert weighs in with some knowledge of oceanic drift patterns, I would be cautious in reading too much into these distances. In addition to ocean currents, certain objects may be affected by surface winds as well. One would expect a difference in motion between objects which are partially above the water (and thus exposed to wind) versus objects that are more or less level with the surface.