Surging and ovulation

Through blood testing and u/s my fertilty clinic found that i surged on July 14. That would mean i would have ovulated in the next 24-36 hours right? Fertility friend indicated that i ovulated on July 15 which woudl be in line with the 24-36 hour thing. However, this morning as i entered in my temperature to fertility friend it detected a chang in my ovulation date to July 20. Can this be? Can you actually ovulate 4 days after a surge?