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ATC operators can suppress skin tracks on their displays if they want. All tracks and "primitives" are recorded and can be played back later, like on CNN. (An FAA "primitive" is what the Navy calls a "contact", a set of radar echoes (typically 16-120) from a single scan that pass a series of tests to designed to reject noise and short lived clutter.) If a primitive doesn't correlate with something on the next scan, it is rejected.

On radar I've worked on, primitives are never shown on an ATC display. (They are available on a maintenance display, along with Canada Geese or clutter from power lines.)

ATC radar that I've worked on will not associate two primitives, - i.e., start a track - on any target moving faster than 600 NM/HR. ATC primary radar in the US only track in two dimensions, range and angle, the only source of altitude information is in the secondary radar (transponder) replies.