Is it that different?
Cave divers receive certifications...etc, etc.
The card you get for, say, Solo, is a card certifying that you took the class and presumably met the standards. It is not a "certification level" in the language of the agencies. It is a specialty certification.
I'm sorry that is confusing to you.
This is why the water is this thread is so muddy: not only do people want to compare the certification levels of different agencies (for example, in SSI the rescue class is a specialty cert, not one of their certification levels); they want to talk about their training levels (like CCR, or Trimix, or Solo) as being "higher" that (say) AOW. Apples and Oranges.