Chris,
What you call a "third or fourth definition" is actually the correct definition when used in this context. This is akin to folks who choose to confuse the scientific definition of the word "theory" with its more common, inappropriate definition.
Just as the word "theory" has a very precise definition when used in a scientific context, so does the word "anecdotal."
In a scientific context, all reports based on personal observation are called anecdotal reports and that is exactly how they are described in the hobby literature.
If one were to perform a search on Reef Central of all the posts by members reporting their personal observations of
Entacmaea quadricolor being accepted or rejected by
Amphiprion percula, that report would be based on "anecdotal evidence," even if each post was accompanied by a photograph documenting the event.
P.S. -- The definition you quoted applies to court cases: 1) Evidence in the form of an anecdote or hearsay is called anecdotal if there is doubt about its veracity: the evidence itself is considered untrustworthy or untrue.
The correct definition, when used in this context, is: 3. based on personal observation, case study reports, or random investigations rather than systematic scientific evaluation: anecdotal evidence.
Whenever a member of Reef Central posts something to the forum based on personal observation of their tank or another tank, that is an anecdotal report.