diff --git a/tools/version.sh b/tools/version.sh
index 8bd1686..4eb2309 100755
--- a/tools/version.sh
+++ b/tools/version.sh
@@ -1,22 +1,34 @@
 #!/usr/bin/env bash
 # Compute the rolling project version: YY.MM.NN
 #   YY.MM : year.month of the current date (e.g. 26.09)
-#   NN    : number of commits since the version tag vYY.MM (e.g. v26.09).
-#           00 when the tag does not exist yet.
-# Output: 26.09.00
+#   NN    : number of commits since the monthly version tag (e.g. 26.09).
+#           00 when no such tag exists yet.
+# The monthly tag is looked up without a "v" prefix (the project
+# convention -- the raw tag name is what sas_py's
+# setuptools-git-versioning turns into the PyPI version); a "v"-prefixed
+# tag is accepted as a fallback.
+# Output: 26.09.05
 set -euo pipefail
 
 YYMM="$(date +%y.%m)"
-TAG="v${YYMM}"
 
+# Echo the first existing monthly tag (bare YY.MM, then v-prefixed).
+find_version_tag() {
+    local t
+    for t in "${YYMM}" "v${YYMM}"; do
+        if git rev-parse --verify "refs/tags/${t}" >/dev/null 2>&1; then
+            printf '%s\n' "${t}"
+            return 0
+        fi
+    done
+    return 1
+}
+
+NN=0
 if command -v git >/dev/null 2>&1 && git rev-parse --git-dir >/dev/null 2>&1; then
-    if git rev-parse --verify "refs/tags/${TAG}" >/dev/null 2>&1; then
+    if TAG="$(find_version_tag)"; then
         NN="$(git rev-list "${TAG}..HEAD" --count 2>/dev/null || echo 0)"
-    else
-        NN=0
     fi
-else
-    NN=0
 fi
 
 printf '%s.%02d\n' "${YYMM}" "${NN:-0}"