Based on the search you described, at first glance it would appear that you shouldn't have received those results, but if you'll humor me for a moment, I'll try to explain why you did.
The hyphens make all the difference. (huh?)
Based on what's listed for Mary Margaret Cowan (Cowan-660), there is a birth year of 1936 and no death date (still living I presume). The results, however, show Mary Cowan (Cowan-65) with no birth date and a death year of 1839 and Mary Cowan (Cowan-76) with no birth date and a death year of 1874. Since neither of the profiles that were returned had a birth year to compare to Mary Margaret Cowan (Cowan-660), technically the results are correct.
Sometimes when you get what would appear to be strange results, you have to look closely to see where the dates fall, before or after the hyphen (birth date - death date) for it to make sense.
Hope this helps!