Hi, It looks like somehow the following defunct test DOI `10.1162/153244303322753616` pops up in multiple references: - https://opencitations.net/index/coci/api/v1/references/10.1186/1758-2946-3-11 - https://opencitations.net/index/coci/api/v1/references/10.1109/TGRS.2011.2107744 - https://opencitations.net/index/coci/api/v1/references/10.1109/TCSVT.2012.2211935 (and probably other ones...) I did not investigate the reason but it looks strange.