accidentals on shared note heads

Could not find a definitive answer in search so asking for clarity. Sorry if this was already answered. The image below shows a shared note head between two voices with a D natural. There are two accidentals, one for each voice. Can I assume if only one accidental is shown, one of the notes does not have an accidental applied? I ask this because in editing a copied measure and moving the notes up or down in tone, the notes always display two accidentals, but at times if I am in insert mode and the existing note already has an accidental, inserting a note from another voice with the the duration and matching accidental selected, the note is inserted on top of the existing note, but only one accidental is shown. Further the playback exhibits no dissonance that occurs when the notes are not equivalent in tone. In other words are there any situations where matching shared notes are shown with only one accidental, or if each note has an accidental, both are always shown. I assume if you only show one accidental that applies to both notes, it is impossible to tell whether one note is unmarked or not.