Messiaen's Prelude for Organ (no opus number, discovered posthumously in 1997, composed probably circa 1929) is rife with ambiguous accidentals. Some can be figured out by examining similar passages, but two cases are particularly egregious:
In bar 59, alto, are the unmarked G noteheads flat or natural?
In bar 61, alto, is the last G sharp or natural?
Asked another way: at those chromatically altered unisons in soprano and alto, which accidental applies to which voice? Is there a rule for that? If we knew the alto's accidental, we could then let it continue for the later alto notes.
(Were the note heads (or the staves!) separate, with an accidental immediately preceding each, the confusion would vanish.)
Explanations from the musical text, from a facsimile edition if such exists, or from rules of notation outweigh reports that so-and-so played it in such-and-such a way.