Temple Grandin and Oliver Sacks; differences of opinion on face-blindness

"You take out some social circuits and get geek circuits, and that seems to be what happens, because the core deficit in mild autism is face blindness, which I have," she explains. "I don't recognize faces until I know people well."
http://www.latimes.com/news/science/la-sci-temple-grandin-20130611-dto,0,2848012.htmlstory

"I’m so bad at recognizing faces that I have to remind myself, “He’s got a goatee” or “She’s wearing black glasses.”
http://www.thedailybeast.com/articles/2013/05/03/temple-grandin-my-big-idea.html

and these quotes about being unable to recognize faces are consistent with what the celebrity autist Temple Grandin wrote right at the beginning of her new book. In the prologue of The Autistic Brain on page vii Grandin wrote that

"My many brains scans have provided possible explanations for my childhood speech delay, panic attacks, and facial-recognition difficulties."

and a similar claim can be found in one of Grandin's older books, Thinking in Pictures:

"I often get into embarassing situations because I do not remember faces unless I have seen the people many times or they have a very distinctive facial feature...." (p.69)

but,
there's this quote from the neurologist, writer and prosopagnosic Dr Oliver Sacks from his book The Mind's Eye:

"(Though Temple is a "visual thinker" and can easily visualize complicated engineering problems, she seems to be no better or worse than average at recognizing faces.)" (p. 92, footnote about famous autist Temple Grandin)

It is worth noting that Dr Sacks has claimed to have severe prosopganosia or face-blindness, or to be precise impaired face memory. He wrote about his unusual and difficult experiences at length in his book The Mind's Eye and also wrote a long magazine article on the same subject. He has also claimed that this trait runs in his family and is developmental. I find his account convincing and I accept him as an expert on the subject of prosopagnosia. It might surprise readers of Temple Grandin's books that as a face-blind person Sacks does not regard himself as autistic or having Asperger syndrome. Sacks has explicitly rejected such labels, with justification, because prosopagnosia is not the same thing as autism.

So, the writings of Grandin and Sacks actually disagree on the question of Grandin's face recognition ability, Sacks observing that hers is normal (but not exceptional) and Grandin claiming many times to be impaired in this area. It is worth noting that non-autistic people with average levels of face recognition ability do have embarassing moments when they can't recognize faces, or more commonly, when they can recognize a face but can't put a name or recall the past meeting situation to that face. I should also point out that I have never found any reference in Grandin's books or anywhere else to Grandin being clinically tested or doing a test for face memory, even though tests of this ability created by leading researchers in the field are easily available. This makes me wonder, in light of the fact that Grandin clearly loves doing psychological tests and questionnaires and writing about her results, as is evident in her new book The Autistic Brain. I would have thought a test of face memory would have been the first psychological test that Grandin would have a go at. If anyone knows about Grandin making reference in a published work or interview to her face memory test scores I would love to know about it. Dr Oliver Sacks can claim both qualifications (he's a neurologist) and expertise in the area of prosopagnosia, so I think his opinion about Grandin's face memory ability should get priority. Another point of difference in the writing of Grandin and Sacks is that Sacks makes it clear that prosopagnosia is a specific disability in a specific type of visual processing (a visual agnosia) and not an indication of autism, while Grandin tends to lump face recognition disability in with autistic traits, characterizing it as a common feature of autism.

Core features of autism are supposed to be an inability to function socially and an inability to empathise and read emotions, so in light of the fact that Grandin claims to be poor at face recognition, it seems all the more remarkable that she apparently can recognize facial expressions:

"I find the same inability to think about children’s strengths in their parents. I’ll say, “What does your kid like? What is your kid good at?” and I can see the confusion in their faces."
http://healthland.time.com/2013/05/19/excerpt-author-temple-grandin-reports-on-the-autistic-brain/

So what gives?