Not every location organizes records in the same way. A marriage index indicated my wife's great-grandparents were married in Burlington, Iowa. I had the date, the location, and their names. I figured with the date it would not be difficult to find their actual marriage record.
When viewing the records on microfilm, I assumed they were filmed in order of license number, or perhaps by date. I looked and they seemed to be in random order.
Then I realized that the records had been sorted by the name of the groom!