Bantamweight
The clearest example of divisional names meaning different things — nearly eight kilos separate the K-1 and ONE limits.
Bantamweight is where the naming problem becomes impossible to ignore. K-1 caps it at 58 kg; ONE Championship's bantamweight limit sits close to 66 kg. Those are not the same division sharing a name — they are different sports' worth of physical difference, and a K-1 bantamweight moving to ONE would be giving up a weight class or more.
The reason is historical rather than deliberate. Japanese promotions built their divisions around Japanese fighters, ONE built theirs around a Southeast Asian roster with a different weight distribution, and nobody had an incentive to harmonise. The result is that comparing champions across promotions at this weight is close to meaningless without checking the limits first.
ONE also uses hydration testing rather than a simple weigh-in, which changes what the number means again — a fighter who cannot rehydrate to make weight is not carrying the same cut as one weighed the night before.