The real issue is that the "Original Network" field isn't properly used on MDL. There's an "abuse" of it that puts OTT platforms, like Netflix as Original Network for all kind of dramas, regardless of if they truly are originals of said network.
Quick example: https://kisskh.at/52939-can-this-person-be-translated
Alchemy of Souls, MDL original network: Netflix & tvN. Nope, tvN is the only original network, it's not a Netflix Original, but a Netflix Exclusive. Yes that's different. Originals are dramas (co)produced for a network who will retain the rights, while Exclusives are dramas bought by another network to broadcast them exclusively for a limited amount of time. In this case, that's a tvN drama for which Netflix has bought worldwide exclusive rights. It doesn't help that Netflix actively dupes customers by labeling its exclusives as "Netflix Series" and putting a custom intro, passing them as its own while merely buying them.
So, back to MDL, apart from being wrong, what's the issue? Well, Netflix Originals (the ones OP is talking about) and Netflix Exclusives are mixed together in the search, with no way whatsoever to find only true Netflix Originals apart from redlisting all other networks.
This can be fixed very quickly and simply, just don't use Netflix as an Original Network for Netflix Exclusives unless it's a Netflix Original. Unfortunately, there's currently a bug that prevents removing a network if it's alone in the edit field.
Unrelated to Netflix but related to the subject, people also confuse TVING and tvN: all tvN dramas are on TVING, but not all TVING dramas are on tvN. For some reason, most if not all TVING dramas are tagged as tvN on MDL, which is wrong.
For reference for Korea, Netflix Originals + Netflix Exclusives:
https://kisskh.at/search?adv=titles&ty=68&co=3&nt=128&sr=-265,-291,-293,-21&so=date
Netflix Originals only:
https://kisskh.at/search?adv=titles&ty=68&co=3&nt=-2,-3,-4,-6,-33,-37,-81,128,-51&so=date&page=3