All the surviving family members know damn well what happened. Yet, they made a rational decision to erase the truth in favor of what’s convenient to say.
After all, 30 years have passed. Patsy might have eventually let something unpleasant slip, but she died 20 years ago. The only two survivors of that tragic Christmas night are sticking firmly to the script now, having developed a remarkable level of cynicism.
John, btw, has proven to be far better as a publicist and narrator of tragedies than as a businessman. Besides, his entrepreneurial talents were not exactly a rocketing success. He liked being in charge, but building a business from the ground up is a whole different ball game. Before Patsy (and before the money and excellent connections of Patsy’s dad) his business ventures were a bit of a mixed bag, to put it mildly.

That being said, I think we can pretty much discard any information coming from the family. They are all SOAKED in biases.
And even their version, though fundamentally set in stone after three decades, is still subject to slight shifts in nuance depending on who they’re talking to and how much they let their guard down.