Re the comments above: fancy a critic not knowing who they were looking at!
Guess what - we're human too! And we don't always review familiar companies or get that many chances to see a company. Where I am, the ballet company only performs about 4-5 productions a year, so even if I can go to every opening night, I don't see the dancers that often. Plus, not every dancer will perform at every opening.
Certainly, I've had companies where I could recognize almost all the dancers by face, and even by mannerism, body type, facial feature or costume (for instance the type and configuration of elastics a male dancer uses on his shoes - some are very unique and so easily recognizable in a press shot where faces are obstructed). However, that kind of familiarity comes with time, and in my experience, from seeing dancers offstage as well as onstage. These days, one is lucky to live in a city where a company performs enough to get that kind of familiarity, especially when most of us have other full time jobs.
But I just as often may be going to see a company I've never seen before, or haven't seen in many years. I do generally try and look at the dancers' bios online before a performance (and study the program during intermissions), but if it's a new dancer, a poorly updated website, a professional level student being used or a temp dancer, good luck. Never mind the increasing trend towards very dim lighting schemes.