A citation context is a sentence or table cell containing a citation; one paper may supply several. Hsiao and Schneider (online December 1, 2021) studied biomedical open-access texts. Postretraction meant after the calendar year of retraction, excluding same-year citations. Among 13,252 qualifying contexts from 9,122 papers, 722 contexts across 430 papers counted as acknowledging retraction: 611 explicit plus 111 inherited from acknowledgment of the same cited work elsewhere in the same paper. These are written-context counts, not counts of aware authors. Missing acknowledgment does not establish ignorance, endorsement or harmful reliance.