Yes, the strength of the I/E preference varies from person to person, and any type can be slight to extreme in their preference. However, when you look at surface behaviours or traits (acting sociable, or wanting to be amidst activity, or being introspective), that's where you get the "introverted extroverts" or "extroverted introverts" stuff. For example, an ISFJ would likely behave more sociably than an INTP who is just as introverted. Or, an ENFP might be more into self-examination than an ESTJ who is just as extraverted.
So if you look at cognitive functions (do they strongly prefer introverted or extraverted ones, or do they use both almost equally?) that preference is not type related. But if you look at common ideas of introverts and extraverts and try to type based on those, it does seem some types are far more likely to be confused than others. ENxPs often identify with some introverted traits and wonder if they are introverts, for example, even if their self-descriptions sound very extraverted to me.