In the article "Universal Densities Exist for Every Finite Reference Measure" (IEEE Trans. Inform. Theory, vol. 69, no. 8, pp. 5277--5288, 2023) we neglected to mention relevant contributions of Boris Ryabko. We cited a source by him that contains a construction of the universal density that we claimed to be our own invention without checking the source after drafting the article. Our article was motivated by a preprint by Feutrill and Roughan, about which we had learned when reviewing the PhD thesis by Andrew Feutrill. Whereas we were not allowed to contact Feutrill and Roughan besides the review form, we developed some ideas of theirs further, ignoring that we stepped into the area previously researched by Ryabko. Our published results exceed those by Ryabko but the article should have been refocused to report Ryabko's contributions. In this note, we detail our citation mistakes.