Let's talk about the plurals of compound nouns. I submit to you: passers-by, hangers-on, attorneys general, brothers-in-law, and culs-de-sac. What about "month end" how would that be pluralized?

We can demonstrate the link between two nouns either by using possessive forms (the US bank's finance division / the finance division of the US bank) or compound nouns (the US bank finance division).