One Question

For those who read Harry Potter:

The ownership of the Elder Wand could only be attained by defeating the previous owner. Gellert Grindelwald stole the wand from Gregorovitch. So even if Grindelwald now had the wand, Gregorovitch was still the owner as he had not been defeated by Grindelwald. Albus Dumbledore defeated Grindelwald and took the wand. But Gregorovitch was still the owner as he had not been defeated. Voldemort killed Gregorovitch. So shouldn't the ownership of the wand have transferred to Voldemort and not Dumbledore?