French language Q&A Forum

Wasn't sure which forum to ask this question as it relates to a different topic but this is the attached forum so I'll ask it here:

The statement and translation :

J’ai un cheveu blanc. – Non, tu as plusieurs cheveux blancs !

I have one white hair. – No, you have a few white hairs!

In this example the word ‘plusieurs’ was used to mean ‘a few’ but in the lesson “Quelques, plusieurs, de nombreux = A few, several, many (quantities), ‘plusieurs’ means several and quelques means ‘a few’. Is there a nuance in usage here?

Firstly - thanks to the creators of this lesson!

Secondly - I am having trouble understanding the distinction between the usage of "Manquer de..." and the impersonal "Il manque...à..."

The lesson describes how the two structures are formed (and gives translations that seem to overlap - e.g. "to lack [something]" VS. [someone/something] is missing (i.e. lacking) something), but doesn't seem to describe how exactly they are used differently from each other.

Thus, I'm wondering if someone can explain in what scenarios "Manquer de" must be used and not "Il manque...à..." (and vice versa), and describe if there are any situations in which both can be used.

(For an example of what I mean, can one say both "Il manque un bouton à ta chemise" (given in the lesson) and "Ta chemise manque d'un bouton" ? Why or why not? Etc.)

Thanks in advance!