Vasectomy Help Please?

My husband had a vasectomy about 7-8 weeks ago. He had his first semen ysis and it noted no sperm present at all. His dr. always wants 2 negative tests. So he had his second test 6 days later, on this past wednesday. We got the results on paper that night. We missed the call from his dr.s office, so we went in the medical center and had them print results. Word for word it says, "No Spermatozoa observed. Round Cells present. Round Cells could be immature germ cells or white blood cells." So great, we have unprotected all weekend from Wednesday to last night. A nurse calls today and says that his dr. needs to call us tomorrow, and that there was a mix up in ONE of the test results that were 6 days apart. She then stated that immature germ cells are in fact immature sperm cells. What the hell? I have read immature sperm cells can't get you pregnant, but this nurse is saying they can. Can anyone help? She says there has to be a mix up because the one 6 days sooner said there was nothing but regular cells. So we are waiting on the dr. Should we be worried about an unwanted pregnancy? We have 2 daughters, aged 4 years, and 5 months. We didn't want anymore. Please help with the issue of these cells. Thanks so much.