I don’t think this statement is correct
Duplicates were flagged for years by curators with no issue. I believe that official guidance was to flag these and leave them unresolved. (Some evidence here: (Duplicate observation - Check if it’s actually a duplicate. Sometimes the user has uploaded the same photo but observed 2 different organisms. Otherwise, iNat staff have instructed us to flag duplicates and leave the flags unresolved.)
The Curator Guideline guidance was changed in 2022 to “prohibit” this, but even as far back as 2019 " “For duplicate observations, please ask the observer to address the issue instead of adding a flag, because site curators cannot remove observations.”"
@bouteloua probably knows the history of this better than me.
There was also a lot of variation in understanding of what a “duplicate” meant back in the day (same photo uploaded by same user vs. sequence of photos taken at the same time by the same user uploaded singly vs. same organism uploaded by multiple users). Duplicates flags are a mix of all of these (and more!) because even curators weren’t clear on what was best/ok/not ok. The guidance on this has now been clarified as well (thankfully!).
There’s a lot of previous discussion on the forum that is relevant:
https://forum.inaturalist.org/t/create-a-flag-category-for-duplicate-observations/29647
https://forum.inaturalist.org/t/create-a-way-to-flag-duplicate-observations-and-remove-rg-status-from-the-extras/201
https://forum.inaturalist.org/t/an-abundance-of-duplicate-observation-flags/32582
https://forum.inaturalist.org/t/what-is-the-appropriate-response-action-for-a-user-uploading-multiple-duplicate-images-organisms/3041
and even back to the old Google Group as above…
All that history aside, I don’t have an issue with going back through and “adjudicating” the flags according to the current guidance, I just don’t personally think it’s a high priority. I think that is one of the main reasons for the current guidance that these are generally left unresolved. I don’t even know that there needs to be any change in the written policy? The current guidance certainly doesn’t prohibit a curator from addressing duplicate flags if they want to. But I think that there’s more of a benefit to the site/community from curators addressing more recent flags that are on observations more likely to be seen/interacted with or affect issues that the community is telling us about now (taxonomy, conservation statuses, problematic posts, whatever).