User blog comment:Skeith9/Heroic Spirits Speculation/@comment-4572759-20140702190817/@comment-24762556-20140704034442

EX doesn't have a limit cap where something becomes "above EX", EX is just "this rank cannot be rated by the regular A-E tiers either because doesn't qualify within the limit of this tiering system", perhaps because it's too strong(Ea), hard to measure with reliable numbers(Hetairoi), if anything "weaker than E" would also qualify as EX.

In essence the EX rank should as well be called "N/A" rank or "???" to make this point more obvious and avoid people interpreting it as "uber A" as they tend to.