Only three fighters in history have 20 or more wins and have avenged all of their losses.
Gilbert Melendez is the only fighter with 20 wins to avenge both of his losses once (total_loss-avenged_loss = 0).
Georges St. Pierre avenged both of his two losses, but later beat Hughes twice (-1). He is the only 20 win fighter to drive the point home and end up with a net difference of less than 0.
Miku Matsumoto had an interesting journey onto this list. She lost to Misaki Takimoto twice, then went on to beat her twice. She also avenged losses to Lisa Ward and Carina Damm (0).
Bas Rutten almost made the cut. He lost four times, twice to Ken Shamrock, both of which he did not avenge. Though he did return to beat Funaki once and Frank Shamrock twice (+1).
Yuka Tsuji (sort of) backdoors her way into the discussion. She avenged her early loss to Ana Michelle Tavares, but later lost to Mei Yamaguchi. Though, she did hold a prior win over Yamaguchi. There may likely be other instances of this as well.