Hmmm, it's hard to explain the title,but it's like... Take a fighter that has two parts of their career. One part was them in their prime,fighting fighters from the era where they're still quite young/priming,70s for example. Then the second part came and they're fighting the new crops of fighters,the 80s guys and so on,but they still dealt well with the new crops,whether it being competitive,winning a title or anything impressive. My favorite non-obvious example here is Shoji Oguma,he firstly fought in a very tough era,he fought three great technicians that are at the very least borderline HOF,but only won and drew one fight out of 8 fights vs the following: Alfonso Lopez(0-1) Betulio Gonzalez( 1-2-1) Miguel Canto (0-3) Counting the ko loss in his record vs Kimio Furesawa, it's official he lost 7 out of 9 fights vs world level fighters. But Oguma actually improved his style a bit,from a flat footed stalker trying to lead with his one-two and punch em out,to a two fisted counterpuncher with slick food movement,he did show it a bit for Betulio 3-4,and Canto 3... Then the 80s came, Chan Hee Park has destroyed the fading but still great and good Canto,and Oguma is fighting on Chan's turf,but he pulled an upset with completely befuddling Chan all the way until the 9th round where he punched him out with his counters. He managed to defend his title a few times,until his luck ran out as he got into a slugfest with Antonio Avelar in round 7 and got ko'ed,he did went competitive a bit in the Watanabe fight but he truly had nothing left in the end. Any more examples?
Marvin Johnson Jerry Quarry had a better record against '70s guys than he did against '60s guys, but the '60s guys were still hanging around to hand him the occasional defeat in the '70s.