Ultrasound Dates

I had an US at 6.5 weeks, one at 13 weeks, and another at 16 weeks. They were all within a few days of each other. I'm trying to figure out when I ovulated. The 6.5 week scan put me ovulating on Oct. 18, the 13 week scan put me O on Oct. 15, and the 16 week scan put me O on Oct. 16. Is it safe to say I ovulated between Oct. 15-18, or could it have fallen out of that range?