Do the results of a semen ysis vary from day to day?

My husband had a vasectomy reversal about a month ago (it's only been a year since the original vasectomy, we are both 26 years old, and have had 2 children together). We took his first semen sample in today and the results were "negative". I know that this is very common for a first ysis, but I was wondering if the results vary from day to day. I was also curious as to what a "negative" result means, specifically. Thanks!