diff --git a/R/peers.R b/R/peers.R
index 66e52ad..82ddf0c 100644
--- a/R/peers.R
+++ b/R/peers.R
@@ -143,9 +143,12 @@ cog_find_peers <- function(target_govid,
 #' @param adjust_to_year Integer base year for CPI-U conversion or `NULL`.
 #' @return Tibble matching [cog_spending()]'s columns, plus a `role`
 #'   column taking values `"target"`, `"peer"`, `"summary_p25"`,
-#'   `"summary_p50"`, or `"summary_p75"`, and `target_rank` (target's rank
-#'   among target+peers at `max(years)`, NA for other rows). Provenance
-#'   attribute reports `verb = "cog_peer_compare"` and `peer_count`.
+#'   `"summary_p50"`, or `"summary_p75"`, `target_rank` (target's rank
+#'   among target+peers at `max(years)`, NA for other rows), and
+#'   `cohort_year` (the year used to build the peer cohort, read from
+#'   `attr(peers, "cohort_year")`; `NA` when `peers` was a bare character
+#'   vector). Provenance reports `verb = "cog_peer_compare"`, `peer_count`,
+#'   `cohort_year`, and `cohort_govids`.
 #' @export
 cog_peer_compare <- function(target_govid, peers, category, years,
                              per_capita = TRUE, adjust_to_year = NULL) {
diff --git a/man/cog_peer_compare.Rd b/man/cog_peer_compare.Rd
index f08d596..a4d9f96 100644
--- a/man/cog_peer_compare.Rd
+++ b/man/cog_peer_compare.Rd
@@ -31,9 +31,12 @@ population.}
 \value{
 Tibble matching [cog_spending()]'s columns, plus a `role`
   column taking values `"target"`, `"peer"`, `"summary_p25"`,
-  `"summary_p50"`, or `"summary_p75"`, and `target_rank` (target's rank
-  among target+peers at `max(years)`, NA for other rows). Provenance
-  attribute reports `verb = "cog_peer_compare"` and `peer_count`.
+  `"summary_p50"`, or `"summary_p75"`, `target_rank` (target's rank
+  among target+peers at `max(years)`, NA for other rows), and
+  `cohort_year` (the year used to build the peer cohort, read from
+  `attr(peers, "cohort_year")`; `NA` when `peers` was a bare character
+  vector). Provenance reports `verb = "cog_peer_compare"`, `peer_count`,
+  `cohort_year`, and `cohort_govids`.
 }
 \description{
 Pulls spending for the target plus a peer set (either a