200 million xp on the runescape hiscores

This may seem like a ridiculous question but: how are players with 200 million XP in a certain skill ranked on the hiscores? I appreciate that it is in the order upon which they gained 200 million in the skill, but why, in some cases, are players who are ranked 1st in a skill moved down to 2nd, even though both them and the person who has overtaken them have 200 million XP?

I know this may be confusing so here’s an example: JC Marlin was once 1st in Agility, with 200 million XP, however recently he has been overtaken by Islam Peace; how? Another example is Firemaking: A Log Burner was once 1st with 200 million XP, now Empror1 is…?

Thanks for your time and if you know any reasons why this is I’d love to know – it’s really been bugging me!