^^ exactly. Unless you were tracking ovulation beforehand you won't know.
You can't - not exactly, anyway. Sounds like those dates are a little off anyway, an LMP of 6/28 should result in a due date of 4/4... but regardless, conception generally occurs somewhere around 14 days past LMP. Anywhere between 7/9 and 7/15 is your best bet but it could be somewhere slightly before or after those dates - not everyone ovulates exactly on the same schedule.