I also think some of the questions are very open for interpretation, for example on the matter of what counts as an empire.
For example there there is a lot of controversy of what the first empire is, according to who you ask. If you look at Europe historically there was only one Empire, the Roman Empire, the first and only empire - untill others claimed to be the succerssors of Rome. Still, the whole idea of 'empire' in Europe comes from Rome.
I am sure there are other questions open for interpretation, for example what counts as a 'global' empire, however I think you get the point.