I think that what we (and the general public) need to understand is that there are many, many kinds of dementia.
And that some patients seem to develop more than one kind of dementia.
The public also needs to know that the speed of onset and that of deterioration both very greatly between one person and another.
One useful rule of thumb is that when someone on the young side (60s) develops dementia, their life expectancy is much shorter than that of an 80 year old who gets it. The 80 year old often lives for 10 years with a diagnosis, whereas the 60 year old usually lives for 3 - 5 years.
Finally, it's helpful that everyone understands that no definitive diagnosis actually can be made until the patient is dead.
It's how we respond to the individual in front of us that makes the difference, though, as we all know.