I've had almost no one argue that I'm not a 4a...
My curl pattern, in April after being sort of shingled.
My hair in March, unstretched, and undefined.
The back in March, unstretched, undefined.
A puff from 2007
Now, my coils are clearly 4a, and that's the only barometer used when determining "hair type." I might be considered a "silkier" 4a than some, but as you can see, I could also be considered a "spongier" or "coarser" 4a by others, depending on how my hair looks at a given time. My strands are fine and my hair overall is thin, so I'm not going to look like those thicker stranded 4as.
I do think that many "4as" could appear to be "3cs" or "4bs" as well, depending on hair style.