What specific record do planets like Neptune and Uranus hold, which distinguishes them from Mars's visitation count?

Answer

Most distant planet visited by a spacecraft

While Mars accumulates the most visits, planets like Neptune and Uranus hold records for the distance visited by a spacecraft, despite only having been reached by flybys.

What specific record do planets like Neptune and Uranus hold, which distinguishes them from Mars's visitation count?
Spaceexplorationplanetsolar system