Always keep in mind that there may be multiple records that may provide information on the date of an event. The date of your ancestor's death may be in a county book of death records, an obituary, a church register, a tombstone, the family bible, his pension record, etc. There may be a note that he is deceased in a deed, a tax roll, or a probate journal.
Not all of these records are equally reliable. Just remember that an event may be recorded in more than one place.
And don't neglect to check records just because "I already have that." One never knows what additional information a similar source may provide.