It appeared on the US Open web page (as shown above) the first week of April, 2019, about three weeks before the event and ten weeks after the field was full. It was only the total that was announced over a year before the event.... I don't see where the prize money breakdown is posted. ...
I guess my point is that "Matchroom is running a nine ball tournament in Las Vegas with a $300,000 prize fund guaranteed" is enough info to get the field they did. I hope any player who is unhappy with the breakdown lets Matchroom know.