... how many boxers could at that stage claim to hold at least one win against every opponent, they had faced until then?
Jimmy Wilde is the only one I know of. I presume there's some unknown journeyman devourers who accomplished a similar feat though. I'll guess 4.
Pretty sure Ray Robinson is one of them (LaMotta being the only loss in his first 100, avenged multiple times). Could Marcel Cerdan be the other? (Common link sort of being LaMotta but I know Mercer already had 100 fights before they met so not avenging that one doesn’t factor into the question).
Robinson drew with Jose Basora in his 55th fight, which he later "avenged" with a 1st round ko - but not until his 114th fight. So Robinson can't be one of them. Also Cerdan lost an early fight against Harry Craster by DQ, which he never avenged.
high number of fights, low number of losses against anywhere from 50 to about 85 different opponents, who knows. Could be a good few, however the thread seems to suggest there have been only 2 fighters... No idea. McAvoy(?).
Steele, Yarosz, Monzon, McAvoy, McFarland, Britton... they all had losses, draws or NCs in their first 100 fights, against opponents they didn't beat at any point during those 100 fights.
Not only did Pedro Carrasco beat every man he faced in his opening 100 pro fights, he ended his career having beaten every man he ever faced.