You are not correct in your assertion that the plural noun requires an apostrophe when used as a plural noun.
Plural noun requires plural verb, not an apostrophe.
Notice in this Wikipedia clip, “Allies” is used with the plural verb “promoted” as in “Allies promoted” and not “Allies’ promoted.”
Likewise, in the second example, “Allies” does use the apostrophe because it is showing possession, “allies’ side.”
https://en.m.wikipedia.org/wiki/Allies_of_World_War_II