
The sperm from a fit dog should live for up to a week, so one day would not have made a real difference unless it was AI from frozen semen.
The bitch won't actually get pregnant until at least two days after ovulation. So when did she actually ovulate as opposed to when the vet said to bring her.
A slip mating with full contact for five minutes is certainly enough of itself as a second mating, as long as you know the dog had been 'working' (ladder climbing).