Requested feature overview description.
When reporting a comment, image/post, or forum post, a check is done on the flag history or ticket system. If a match is found, then return the last ticket or flag reason.
Implementation notes:
If it is a comment/forum post, just return the ticket.
If it is a post, then add the text "This post has been previously flagged and the flag was denied.". This can also be used to notify the user before they report a post older than 1 month.

Regardless if it was flagged, if it was old, or not, this should not prevent the user from flagging or reporting a post or comment. There are various reasons such as dead domains being hijacked and redirecting to malware sites, and what not.

Examples:

• https://i.gyazo.com/7cf685b64f81d5ad7f717a31a74d4789.png
• https://i.gyazo.com/88e7ae771d919c989d0dca3681654ed2.png

Why would it be useful?
I believe it would help both users and admins/mods, especially the mods on having to re-close previously flagged stuff.

What part(s) of the site page(s) are affected?

• Flagging and Ticket system

--edit--
I forgot the title, woops.
Also I am not good with words, "the flag was denied" sounds wrong to me but it might be the correct wording.

I was just thinking about this myself.

For comments on posts, forums and blips, how about having the report button disable once it has been used (similar to how the previous/next buttons are disabled on the first/last posts in pools)?

Also, what about putting a time limit on the report button of the allowed 6 month period (like the limit set on the edit button on comments)?

The only concern I have is that this:

Chaser said:
Regardless if it was flagged or not, this should not prevent the user from flagging or reporting a post or comment. There are various reasons such as dead domains being hijacked and redirecting to malware sites, and what not.

may still be an issue (Although if such a link is found it would probably be best to alert a currently online admin directly about it rather than placing it in the ticket queue).

+1, I've seen tickets end with "recently handled" or "check the user's record", etc., and flags (I'm a guilty party of) that are reflagged before reading the description/comments. This would be a great way to exclaim that it's already been handled.

Definitely a good thing. As long as it was not preventative in regards to comments.

Perhaps giving users a notice and then offering a choice whether to report still or not without disclosing the original ticket for privacy reasons.

For example if multiple users report a comment there's likely a really good reason for it to be reported.