Unhandled reports might be revisited, since if the mod clicks ignore on a report, then that only ignores it for them. So, another moderator might see it in their report queue, and decide to act upon it. Although, once the period for displaying the report in queues is gone, then yeah unhandled reports aren't revisited, unless they're reported again in the future. As far as I know, if that happens, and it is then handled at a later date, it doesn't correct the initial report that was marked as unhandled. Although, I can't say I've ever monitored that, I'm just going on a logical assumption.
So, there's two ways of not handling a report. Either ignoring it (clicking "ignore" which removes it from your report queue) or by just
ignoring it without actually clicking ignore, if that makes sense. So, the latter example would be not taking any action at all, whereas clicking ignore is technically an action which only really effects your report queue not anyone else's.
I'm still not sure what you meant when you said that some cases are best left unhamdled
I've been meaning to do a detailed write up on my reporting effectively thread on when unhandled reports are actually the logical way of
handling a report. Just haven't got around to it yet. It's on my to do list for this year
.