The most accurate writing requires the use of the grave stress over open vowels and the acute stress over closed vowel. Nevertheless, to make a distinction between open and close vowel has a meaning only for "e" and "o", which both can be open as well as closed; indeed "a" can be only open, "i" and "u" can be only closed. On the other hand, being the accent mandatory only for words that are stressed on last syllable and a few monosyllables that are homophones, the use of acute accent over "o" vowel is limited to very few words, Italianizations of French word like "bordó" [bordeaux] or "trumó" [trumeau].
All this makes that a real distinction is needed only for the vowel "e" and, in the common use, has entered the practice of stressing all the other vowels with the grave accent.