> found that they can recognise and remember at least 50 individual faces for more than 2 years. That is longer than many humans.

What? I was under the impression that humans could generally remember long-term hundreds of faces, if not thousands. You may not always be able to remember everyone's name, but you remember their face.

The idea of someone not being able to remember even fifty individual faces sounds bizarre to me, unless we're talking about a person with a serious mental handicap.