Once you get an exotic armor piece in your collections, regardless of how it was first obtained, it then becomes a part of the general exotic lootpool.
In particular, pretty much all exotic armor from Y4 onward requires you to run lost sectors just until you get it the first time, then they'll potentially drop from anywhere.
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Oh....had no clue. Thank you!!! Would be nice to get a NEW exotic though lol already ran lost sectors for it
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Well, the fact that you got Necrotic Grips from Xur means you've already gotten every possible world drop exotic (thus far) from him, so the only "new" ones left are those locked behind lost sectors or ones tied to a quest (such as the Shadowkeep exotics).
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Oh snap. Thanks again!