Previous research has posited a correlation between poor indexing and inadvertent post-retraction citation. However, to date, there has been limited systematic study of retraction indexing quality: we are aware of one database-wide comparison of PubMed and Web of Science, and multiple smaller studies highlighting indexing problems for items with the same reason for retraction or same field of study. To assess the agreement between multidisciplinary retraction indexes, we create a union list of 49,924 publications with DOIs from the retraction indices of at least one of Crossref, Retraction Watch, Scopus, and Web of Science. Only 1593 (3%) are deemed retracted by the intersection of all four sources. For 14,743 publications (almost 30%), there is disagreement: at least one source deems them retracted while another lacks retraction indexing. Of the items deemed retracted by at least one source, retraction indexing was lacking for 32% covered in Scopus, 7% covered in Crossref, and 4% covered in Web of Science. We manually examined 201 items from the union list and found that 115/201 (57.21%) DOIs were retracted publications while 59 (29.35%) were retraction notices. In future work we plan to use a validated version of this union list to assess the retraction indexing of subject-specific sources.