Why some compounds cannot be downloaded?

I was trying to download binary and ternary oxides from MP by using API. Before I got around 24293 compounds but now I am able to get only 23313. I cannot download some compounds like ‘mp-761803La9Ni5O19’ ? Why? I am using the same script except for new property “e_above_hull”.

from pymatgen import MPRester
api = MPRester(api_key=“mykey”)
criteria={“elements”:{"$all": [“O”]}, “nelements”:{’$lt’:4}}
properties=[“pretty_formula”,“cif”,“material_id”, “formation_energy_per_atom”, “band_gap”, “e_above_hull”]
c = api.query(criteria=criteria,properties=properties)

Hi @Hemanta

When did you last download the compounds? They might have been merged with other materials are we are improving our duplicate checking routines. We’re trying to build a consistent DB where each material is represented only once. Unfortunately, this is a difficult task as even DBs such as the ICSD have many duplicate entries and structure matching can be a difficult task.

Thank you so much for the response. First it was almost a year ago and I downloaded it again a week before. For example compound ‘mp-761803La9Ni5O19’ is there in the database, but I cannot download it. In addition could you please describe what exactly the duplicate means, is it the same compounds with different material ID or compounds with similar compositions and similarity in some properties? Can you give some examples of compounds which you consider duplicate in the list and structure matching process used to identify the duplicates? Thanks again.