For the moments worth dressing up for

What began as one designer’s vision in 2008 has grown into a global name in formal wear — the gown remembered from prom, the dress on the pageant stage, the look that lands on the red carpet.

Twenty-one collections have shown at New York Fashion Week since 2011. What walks that runway in September is on the racks by winter, in sizes running 000 through 26, at authorized retailers.