It is quite possible that killdisk writes to the hard drive and reads it back and then also possible if the sector is bad marks it as bad, so you do not see it or the hard drive does not use the bad sectors.
1. If the bad sectors were in the first 60 sectors that could be bad, that is were the boot sector lives.
2. chuck it,,, a hard drive with bad sectors is not like you getting a cold. The hard drive will never get over bad sectors, just more and more creep in with possible data loss and the drive letting you down at a bad time. Hard drives are CHEAP. I remeber paying $375.00 for a 454meg ( ..a little under half a gig ) IBM hard drive in the mid 90's.,,and it was on sale.