Does He? Or...Doesn't He?

I often wonder if my dad really has Alzheimer's disease. His doctor performed the MMSE (Mini-Mental State Exam) in 2009 and repeated it recently. A score of 23 or below is indicative of cognitive impairment. My dad scored a 26 both times.When I asked the doctor about her diagnosis, she stated that the 'patterns of behavior' she is seeing lead her to believe that he does indeed have Alzheimer's Disease. Once I asked her to what degree information provided by Jennifer might have influenced her diagnosis. She paused and told me that was a good question, and she wasn't sure. Jennifer, soon to be  my dad's ex-wife, tends to obsess about some things and probably has whined about pointed out all of the behaviors she has seen that highlight my dad's memory issues.
There is no doubt that Dad has very poor short term recall. Some days he will ask me almost the same question three or four times within a few minutes. Often I will be chatting about something I have done, and when I allude to it again, he asks me what I'm talking about. He occasionally misplaces his keys, wallet or a document and can't remember where he put them. He'll put something on his shopping list that he already has in the kitchen, either forgetting he has it or forgetting that he already purchased the item. Is it Alzheimer's or is it age?
Dad decided to divorce my step-mother because she was often away, visiting her family, leaving him by himself. I took Dad to see a number of continuing care retirement communities that have independent living facilities as well as long-term care programs and 'memory care' units that he may need in the future. We found a fabulous facility. The people were great. The location was ideal. The apartments were modern, roomy and appealing. Sadly, because the Doctor reported that my dad had the early stages of Alzheimer's, this particular community denied my father's entrance. How frustrating! How demoralizing for Dad. How does she know for sure?