Fiirst example that comes to mind -
On 23 May 2005 Kay Clegg posted a message that included the follwing information:
"I sent for LDS film 1559456 and found in the Douglas Borrough Cemetery in graveside number NP3 COLLISTER, Margaret died 29 November 1935 age 71 ..... Also in the plot was COLLISTER, Florence Elsie .... and COLLISTER, Thomas. When I went to the page that NP3's monumental inscription should have been listed on, there was no listing." This message was followed by a long thread on the topic.

I have a photograph of the headstone with its inscription.

Two points though: I am assuming the LDS film is of the IOMFHS publication. The omission may have been made by the LDS. However, my point still stands - no listing doesn't necessarily mean no headstone