Vista - WIM format's single-instance storage Q

I am going through every available MS Vista document at this moment, and
summarizing and translating as I will have to instruct others.
anyway, I was wondering about the following; the WIM image has a
single-instance storage technique (meaning that only one unique file will be
placed in it in the case that file is present more than once in the source).
here comes my Q: what does the WIM image do with dlls? the file itself can
be present more than once, but can have different versions.