diff --git a/score/datetime_converter/datetime_converter_test.cpp b/score/datetime_converter/datetime_converter_test.cpp
index 9ea21212b..b5c66e81c 100644
--- a/score/datetime_converter/datetime_converter_test.cpp
+++ b/score/datetime_converter/datetime_converter_test.cpp
@@ -453,6 +453,122 @@ TEST_F(DateTimeConverterTest, test_yearIsLeap)
     ASSERT_FALSE(score::common::yearIsLeap(2100));
 }
 
+TEST_F(DateTimeConverterTest, invalid_month_values)
+{
+    RecordProperty("Description", "Verify invalid month values are rejected.");
+    RecordProperty("TestType", "Negative");
+    RecordProperty("Requirement", "DatetimeValidation");
+    RecordProperty("Coverage", "MonthValidation");
+
+    auto dtt = std::make_shared<DateTimeType>(2020, 0, 10, 3, 4, 5);
+    ASSERT_FALSE(score::common::isValidDateTimeFormat(dtt));
+
+    dtt->m_month = 13;
+    ASSERT_FALSE(score::common::isValidDateTimeFormat(dtt));
+
+    dtt->m_month = -1;
+    ASSERT_FALSE(score::common::isValidDateTimeFormat(dtt));
+}
+
+TEST_F(DateTimeConverterTest, invalid_day_values)
+{
+    RecordProperty("Description", "Verify invalid day values are rejected.");
+    RecordProperty("TestType", "Negative");
+    RecordProperty("Requirement", "DatetimeValidation");
+    RecordProperty("Coverage", "DayValidation");
+
+    auto dtt = std::make_shared<DateTimeType>(2020, 12, 34, 3, 4, 5);
+    ASSERT_FALSE(score::common::isValidDateTimeFormat(dtt));
+
+    dtt->m_day = -1;
+    ASSERT_FALSE(score::common::isValidDateTimeFormat(dtt));
+}
+
+TEST_F(DateTimeConverterTest, dateTimeToEpoch_false_isValidDateTimeFormat)
+{
+    RecordProperty("Description", "Verify dateTimeToEpoch returns false for invalid DateTime input.");
+    RecordProperty("TestType", "Negative");
+    RecordProperty("Requirement", "DatetimeValidation");
+    RecordProperty("Coverage", "ErrorHandling");
+
+    time_t epoch = static_cast<time_t>(0x7F7F7F7F);
+
+    // Invalid: month = 13 -> isValidDateTimeFormat returns false
+    auto d = std::make_shared<DateTimeType>(2024, 13, 10, 12, 30, 45);
+
+    ASSERT_FALSE(score::common::dateTimeToEpoch(d, &epoch));
+
+    ASSERT_EQ(epoch, static_cast<time_t>(0x7F7F7F7F));
+}
+
+TEST_F(DateTimeConverterTest, EpochToDateTime_Pre1970_LeapYear_DaysSumDecrementedInJanuary)
+{
+    RecordProperty("Description", "Verify pre-1970 leap year round-trip stability.");
+    RecordProperty("TestType", "Boundary");
+    RecordProperty("Requirement", "DatetimeConversion_Pre1970_LeapYear");
+    RecordProperty("Coverage", "LeapYearHandling_RoundTrip");
+
+    for (int month = 1; month <= 12; ++month)
+    {
+        for (int day = 1; day <= 31; ++day)
+        {
+            if ((month == 2 && day > 29) ||
+                (month == 4 && day > 30) ||
+                (month == 6 && day > 30) ||
+                (month == 9 && day > 30) ||
+                (month == 11 && day > 30))
+                continue;
+
+            time_t epoch{};
+            auto d = std::make_shared<DateTimeType>(1968, month, day, 0, 0, 1);
+
+            if (!score::common::dateTimeToEpoch(d, &epoch))
+                continue;
+
+            auto dt = score::common::epochToDateTime(epoch);
+            if (dt == nullptr)
+                continue;
+            time_t epoch_roundtrip = static_cast<time_t>(-1);
+            ASSERT_TRUE(score::common::dateTimeToEpoch(dt, &epoch_roundtrip));
+        }
+    }
+}
+
+TEST_F(DateTimeConverterTest, EpochToDateTime_Post1970_LeapYear_DaysSumDecremented)
+{
+    RecordProperty("Description",
+        "Sweep across 1972 leap year (post-1970) to verify leap adjustment and round-trip stability.");
+    RecordProperty("TestType", "Boundary");
+    RecordProperty("Requirement", "DatetimeConversion_Post1970_LeapYear");
+    RecordProperty("Coverage", "LeapYearHandling_RoundTrip");
+
+    for (int month = 1; month <= 12; ++month)
+    {
+        for (int day = 1; day <= 31; ++day)
+        {
+            if ((month == 2 && day > 29) ||
+                (month == 4 && day > 30) ||
+                (month == 6 && day > 30) ||
+                (month == 9 && day > 30) ||
+                (month == 11 && day > 30))
+                continue;
+
+            time_t epoch{};
+            auto d = std::make_shared<DateTimeType>(1972, month, day, 0, 0, 1);
+
+            if (!score::common::dateTimeToEpoch(d, &epoch))
+                continue;
+
+            auto dt = score::common::epochToDateTime(epoch);
+            ASSERT_NE(dt, nullptr);
+
+            time_t epoch_roundtrip = static_cast<time_t>(-1);
+            ASSERT_TRUE(score::common::dateTimeToEpoch(dt, &epoch_roundtrip));
+        }
+       
+    }
+}
+
 }  // namespace testing
 }  // namespace platform
 }  // namespace score