1. every area in the Venn diagram can be expressed by at least one combination.

2. different expression may correspond to the same area.
Ex. (a v b) /\ (a v c) = a v (b /\ c)

3. there are 2 X 2 X ... X 2 areas, so there are that many "different" ("non-equivalent") combinations.

4. there are many ways to define "equivalent", each give you different answers, so you need to specify your "equivalence".
Ex. to some people a v a = a but to some other people a v a =\= a.
to some people a v b = b v a but to some other people a v b =\= b v a
You have to tell what you want

Have fun!