As we have been doing since Firelands, we are keeping the world rankings fair by normalizing the heroic boss kill times for those that had delayed access to heroics. To highlight the issue, we recently saw US guilds kill 50% of the heroic MV bosses before the EU, KR and TW players even had access to the heroics.
How does normalization work? We calculate the time delay in which the regions had access to the heroic content and then subtract this time from the heroic kills. The result is a world ranking where everyone competes as if they all had access to the heroic content at the same time. This, combined with our "you are ranked based on your latest boss kill" approach, provides a powerful guild ranking system - and one that keeps people coming back to GuildOx.
If you still wish to see who killed what boss first, irrespective of delayed access, you most certainly can. Click on the boss kill and then hit the "raw" sort link at the top of the date column. Stone Guard example