As a part-time artist who prints abstract digital art, I’ve had this happen to me - had my art hung upside-down from what I intended in a gallery show. It’s one reason I started signing the bottom right corner of the work, and framing with hanging wire well offset vertically from the center. But in at least one case I remember, I discussed the orientation with a buyer of the work and we agreed that the upside-down mistake actually looked better, and I endorsed them hanging it that way. Sometimes the orientation may be critical to the intent, and sometimes it’s not particularly relevant. It’s too bad we can’t ask Mondrian himself. I don’t know anything about his history or personality, anyone have any idea if orientation really mattered to him or whether he’s the kind of artist that would be open to someone preferring an upside-down version?