When in doubt, disclose more than less. This is not the industry to try and sneak by something like an extra failed check compared to what is on your application. United's interview process is a piece of cake for those that are honest, humble and accountable for all positives and negatives in their lives/career.

It's not so much a line between 3 vs 4 failures, its the notion that you are aware of a failure but trying to skirt around it as it might not be in your log book. That is an integrity concern and would surely bite you square in the bum.

As stated about a friend here with 2 DUI's (likely a mutual friend BTW), he is far from perfect but owned his errors and was able to show how he learned from not one but two pretty big screw up's. Nobody is perfect, but being open and honest is the next closest thing. Best of luck!