DEAD SPERM AFTER VASECTOMY

MY HUSBAND HAD A VASECTOMY IN NOVEMBER 2008.  AFTER 20 EJACULATIONS WE TOOK
THE DOCTOR A SPERM SAMPLE.  THE RESULTS CAME BACK AND THE DOCTOR SAID THAT HE COULD STILL SEE THE SPERM BUT THEY WERE DEAD.  THE DOCTOR TOLD HIM TO COME BACK WITH ANOTHER SAMPLE AFTER 10 MORE EJACULATIONS.  MY HUSBAND THEN TOOK THE NEXT SPERM SAMPLE BACK TO HIM. AND THE SAME THING HAPPENED AGAIN.  THE DOCTOR THEN ASKED HIM TO TRY 10 MORE TIMES AND BRING YET ANOTHER SAMPLE (FOR A TOTAL OF 40 TIMES).  MY HUSBAND TOOK HIM THE SPERM SAMPLE LAST WEEK AND HE CALLED MY HUSBAND BACK TELLING HIM THAT HE COULD STILL SEE SOME SPERM, BUT THE WERE ARE DEAD AND TO COME BACK IN 6 WEEKS.  MY QUESTION IS DOES THIS SEEM NORMAL? AND IF SO WHAT MORE CAN WE DO TO HELP THIS ALONG?
ANY ADVICE WOULD BE GREATLY APPRECIATED!