I find the use of the "Implemented" prefix a bit counterintuitive - I suggest that "Implemented" be reserved for those cases where suggestions actually result in a change to the core functionality and another prefix ("Already Exists" for example) for those cases where the suggested functionality already exists and has not been added in response to a suggestion.
I suppose you could look at it that way but it's clearly two different things (a suggestion causing a change to the code versus a suggestion for a feature that already exists). There's granularity in the "negative" prefixes ("Lack of Interest" meaning less than 3 Likes over a year, and "Not Planned" meaning the Developers are not interested). And there's the neutral "Duplicate" suggestion. "Already Exists" should be another neutral prefix, and "Implemented" should mean that the suggestion led to a change in functionality. Otherwise, when you look at the list of Implemented suggestions in the Closed Suggestion forum you can't tell which were actually successful suggestions and which weren't. It was because I was looking for this information that I realized it wasn't readily available - you'd have to wade through each thread to make such a determination.
If it says it's implemented, then it means it's implemented - does it matter if it was implementated due to a suggestion (although it's usually possible to tell by the replies in the thread as it generally says in there if it's already in there) or if it was something implemented by the devs?
It matters to me else I wouldn't have mentioned it. As I said, it was in looking for the information that I discovered it wasn't readily available. Why would I be looking for the information if I didn't think it mattered?
When a suggestion is made and subsequently marked "Implemented" the inference is that there was causation - the suggestion caused the implementation. The present system is ambiguous in this regard, and could easily be rendered unambiguous by the addition of an "Already Exists" prefix. This way the people who think it matters will get the information they want and the people who think it doesn't matter will be unaffected either way.
Not sure if everyone is following what @The Sandman means, but to clarify:
When someone makes a suggestion for a feature which has already been implemented, as an example; "Please implement an alert system in XF so I can get alerts when someone replies to my thread" we would close that suggestion and mark it as "Implemented".
I don't necessarily agree, but this could imply that this suggestion was implemented as a result of this suggestion thread, whereas actually it's been a feature since forever, or more specifically, already implemented by the time the suggestion was made.
The recommendation here is to have another prefix which would imply the suggestion wasn't valid because it was already a feature.
It's a very good suggestion IMO. As with the prefix in bug reports "not a bug" it would make people do a bit more research before posting and as Sandman says it would be informative for those who are interested, and would take away nothing from those who aren't.