I had always believed that there were two kinds of flares on line ends, perfect and wrong.
I just had an experienced HVAC tech tell me that a flare which has an irregular ridge at the outside edge of the mating surface, as if there was a burr from cutting the copper line and the flaring cone had flattened it out, would "squish right out" when torqued down against the brass fitting in a mini split, and would never leak, not even with 410A. Is he right? Most of the flared surface looked fine, but the raised and slightly jagged ridge at the outer edge would be the first thing to make contact with the fitting on the equipment.
I don't have a digital camera with the macro focusing needed to show you what I'm talking about.