diff --git a/ats_schema_test.go b/ats_schema_test.go
index cdce40c..54d1bf9 100644
--- a/ats_schema_test.go
+++ b/ats_schema_test.go
@@ -409,9 +409,8 @@ func TestATSSchemaBundleMatchesOGC(t *testing.T) {
 // reason is the standard's, not the tier's: `temporalPrimitiveValue` declares
 // `datetimes` an array of `minItems: 2` beside `values` as a single scalar
 // (`oneOf` number/string/boolean), so no document carrying a value per instant
-// satisfies it; and its `interpolation` enum reads Discrete/Step/Linear/Regression
-// where the temporal-geometry half of the same document names Stepwise. This
-// asserts the cell that has one authority, which is the type token.
+// satisfies it. This asserts the cells that are satisfiable, of which the type
+// token is one.
 func TestATSSchemaTemporalPropertyType(t *testing.T) {
 	f, err := os.Open(ogcBundlePath)
 	if err != nil {
@@ -465,3 +464,78 @@ func TestATSSchemaTemporalPropertyType(t *testing.T) {
 		}
 	}
 }
+
+// The interpolation the tier writes is one the standard names.
+//
+// ⛔ BOTH ADMITTED SETS ARE READ OUT OF THE VENDORED DOCUMENT. Part 1 constrains
+// an interpolation in exactly two places and they are not the same list:
+// `motionCurve` (what a temporal geometry takes, through a $ref that a walk over
+// `temporalPrimitiveGeometry` alone does not see) and `temporalPrimitiveValue`.
+// The step function is `Step` in both, and the word `Stepwise` — the older
+// MF-JSON encoding extension's spelling — appears nowhere in the document.
+func TestATSSchemaInterpolationToken(t *testing.T) {
+	raw, err := os.ReadFile(ogcBundlePath)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if n := bytes.Count(raw, []byte(`"Stepwise"`)); n != 0 {
+		t.Errorf(`the vendored document names "Stepwise" %d times; the tier writes "Step" because it named it 0`, n)
+	}
+	var doc struct {
+		Components struct {
+			Schemas struct {
+				MotionCurve struct {
+					OneOf []struct {
+						Enum []string `json:"enum"`
+					} `json:"oneOf"`
+				} `json:"motionCurve"`
+				TemporalPrimitiveValue struct {
+					Properties struct {
+						Interpolation struct {
+							Enum []string `json:"enum"`
+						} `json:"interpolation"`
+					} `json:"properties"`
+				} `json:"temporalPrimitiveValue"`
+			} `json:"schemas"`
+		} `json:"components"`
+	}
+	if err := json.Unmarshal(raw, &doc); err != nil {
+		t.Fatalf("reading %s: %v", ogcBundlePath, err)
+	}
+	var curve []string
+	for _, b := range doc.Components.Schemas.MotionCurve.OneOf {
+		curve = append(curve, b.Enum...)
+	}
+	value := doc.Components.Schemas.TemporalPrimitiveValue.Properties.Interpolation.Enum
+	if len(curve) == 0 || len(value) == 0 {
+		t.Fatal("the vendored document declares no interpolation enum, so this test would assert nothing")
+	}
+	in := func(set []string, s string) bool {
+		for _, a := range set {
+			if a == s {
+				return true
+			}
+		}
+		return false
+	}
+	// What the tier writes: MobilityDB's own token, carried through ogcify.
+	const geometry = `{"type":"MovingPoint","interpolation":"Step"}`
+	const valueSeq = `{"interpolation":"Step","values":[1,2]}`
+	for _, c := range []struct {
+		what, doc string
+		admitted  []string
+	}{
+		{"a temporal geometry", geometry, curve},
+		{"a temporal property value", valueSeq, value},
+	} {
+		var m map[string]any
+		if err := json.Unmarshal([]byte(ogcify(c.doc)), &m); err != nil {
+			t.Fatalf("%s: ogcify produced no JSON: %v", c.what, err)
+		}
+		got, _ := m["interpolation"].(string)
+		if !in(c.admitted, got) {
+			t.Errorf("%s is written with interpolation %q, which the standard does not name; it admits %v",
+				c.what, got, c.admitted)
+		}
+	}
+}
diff --git a/main.go b/main.go
index 09e4509..ee49235 100644
--- a/main.go
+++ b/main.go
@@ -42,8 +42,18 @@ var (
 )
 
 // OGC <-> MobilityDB conventions (assessed against live MobilityDB):
-// MobilityDB rejects "Stepwise" and uses "Step"; crs is "EPSG:<n>" vs the URN.
-var ogc2mdbInterp = map[string]string{"Linear": "Linear", "Stepwise": "Step", "Discrete": "Discrete"}
+// crs is "EPSG:<n>" vs the URN.
+//
+// The step function is "Step" on both sides. OGC API - Moving Features Part 1
+// names it so in each of the two places it constrains an interpolation —
+// `motionCurve` (Discrete/Step/Linear/Quadratic/Cubic, what a temporal geometry
+// takes) and `temporalPrimitiveValue` (Discrete/Step/Linear/Regression) — and
+// the word "Stepwise" appears nowhere in that standard. "Stepwise" belongs to
+// the older MF-JSON encoding extension, and is accepted on input for a client
+// that still writes it.
+var ogc2mdbInterp = map[string]string{
+	"Linear": "Linear", "Step": "Step", "Discrete": "Discrete", "Stepwise": "Step",
+}
 var epsgName = regexp.MustCompile(`"name":\s*"EPSG:(\d+)"`)
 var epsgURN = regexp.MustCompile(`EPSG:+(\d+)`)
 
@@ -55,9 +65,10 @@ var hourOnlyOffset = regexp.MustCompile(`(\d\d:\d\d:\d\d(?:\.\d+)?)([+-]\d\d)(["
 // rfc3339Tz completes hour-only timezone offsets so datetimes are RFC 3339.
 func rfc3339Tz(s string) string { return hourOnlyOffset.ReplaceAllString(s, `$1$2:00$3`) }
 
+// ogcify turns what MobilityDB writes into what the standard names. The
+// interpolation needs nothing: MobilityDB's "Step" is already the token both
+// `motionCurve` and `temporalPrimitiveValue` enumerate.
 func ogcify(s string) string {
-	s = strings.ReplaceAll(s, `"interpolation": "Step"`, `"interpolation": "Stepwise"`)
-	s = strings.ReplaceAll(s, `"interpolation":"Step"`, `"interpolation":"Stepwise"`)
 	s = rfc3339Tz(s)
 	return epsgName.ReplaceAllString(s, `"name":"urn:ogc:def:crs:EPSG::$1"`)
 }
diff --git a/samples/temporal-geometry-velocity.json b/samples/temporal-geometry-velocity.json
index 0f53018..eca97e8 100644
--- a/samples/temporal-geometry-velocity.json
+++ b/samples/temporal-geometry-velocity.json
@@ -11,7 +11,7 @@
         "2026-01-01T08:25:00+00:00",
         "2026-01-01T08:45:00+00:00"
       ],
-      "interpolation": "Stepwise",
+      "interpolation": "Step",
       "lower_inc": true,
       "upper_inc": true,
       "values": [
diff --git a/samples/temporal-properties.json b/samples/temporal-properties.json
index ac79cbb..42d29cc 100644
--- a/samples/temporal-properties.json
+++ b/samples/temporal-properties.json
@@ -55,6 +55,6 @@
       "type": "TText"
     }
   ],
-  "timeStamp": "2026-08-29T17:08:43Z"
+  "timeStamp": "2026-08-29T17:29:23Z"
 }
 
diff --git a/samples/temporal-property.json b/samples/temporal-property.json
index 1b98903..69776a3 100644
--- a/samples/temporal-property.json
+++ b/samples/temporal-property.json
@@ -8,7 +8,7 @@
         "2026-01-01T08:00:00+00:00",
         "2026-01-01T08:45:00+00:00"
       ],
-      "interpolation": "Stepwise",
+      "interpolation": "Step",
       "lower_inc": true,
       "upper_inc": true,
       "values": [