The result was overturned the next day but the rest of the world didn't catch up on this for years. Technically he was undefeated for sure.
But he still lost for 24 hours or so; I guess there are advantages when your manager runs boxing in the area. Chavez was my favourite fighter of the mid/late 80s/early 90s, but as I had an old Ring record book, I never considered him undefeated.
Interested in some other names here, great fighters or not so great ones. How long was it between Pep and Robinson's 1st and 2nd losses?
When Chavez won the title he was something like 41-0. So he still won three championships & won over 40+ bouts against world class competition without a loss.
Some sources have Hal Bagwell (Great Britain) with 175 wins 5 draws 1938-48 Some others have it 180 fights, 175 wins, 2 draws, 3 no decision from 1938-1948 and still others have him undefeated between August 10, 1938, and November 29, 1948, Hal Bagwell of Gloucester, England, fought 183 consecutive bouts without a defeat and only 5 draws. BoxRec has him undefeated in 60 bouts. Buck Smith had a streak of 107, which included 6 No Decision bouts. Packey McFarland had a unbeaten streak of 104, which included 6 draws. Jimmy Wilde was 92-0-2 in his first 102 bouts. Pedro Carrasco had an unbeaten streak of 93 bouts If you don't count No Decision bouts, Harry Greb was unbeaten in 188 bouts from 1916 to 1923 and Johnny Dundee was unbeaten in his first 144 bout if you don't count No-Decision bouts.
Amateur winning streaks and simply time based one regardless of fights are good too. Didn't Jones only have a TKO loss in almost a decade and a half of fighting? I think Hopkin's went a decade undefeated, as did John David Jackson.