diff --git a/gnss/aidl/android/hardware/gnss/gnss_assistance/AuxiliaryInformation.aidl b/gnss/aidl/android/hardware/gnss/gnss_assistance/AuxiliaryInformation.aidl
index f6c6cb9..61b510b 100644
--- a/gnss/aidl/android/hardware/gnss/gnss_assistance/AuxiliaryInformation.aidl
+++ b/gnss/aidl/android/hardware/gnss/gnss_assistance/AuxiliaryInformation.aidl
@@ -21,6 +21,8 @@
 /**
  * Contains parameters to provide additional information dependent on the GNSS constellation.
  *
+ * If svid is -1, the AuxiliaryInformation is not available.
+ *
  * @hide
  */
 @VintfStability
@@ -49,6 +51,8 @@
      * - QZSS:    183-206
      * - Galileo: 1-36
      * - Beidou:  1-63
+     *
+     * If it is -1, the AuxiliaryInformation is not available.
      */
     int svid;
 
diff --git a/gnss/aidl/android/hardware/gnss/gnss_assistance/GalileoIonosphericModel.aidl b/gnss/aidl/android/hardware/gnss/gnss_assistance/GalileoIonosphericModel.aidl
index ced8917..65f840c 100644
--- a/gnss/aidl/android/hardware/gnss/gnss_assistance/GalileoIonosphericModel.aidl
+++ b/gnss/aidl/android/hardware/gnss/gnss_assistance/GalileoIonosphericModel.aidl
@@ -18,7 +18,9 @@
 
 /**
  * Contains Galileo ionospheric model.
- * This is Defined in Galileo-OS-SIS-ICD-v2.1, 5.1.6.
+ * This is defined in Galileo-OS-SIS-ICD-v2.1, 5.1.6.
+ *
+ * If all coefficients are 0, the GalileoIonosphericModel is not available.
  *
  * @hide
  */
diff --git a/gnss/aidl/android/hardware/gnss/gnss_assistance/GlonassAlmanac.aidl b/gnss/aidl/android/hardware/gnss/gnss_assistance/GlonassAlmanac.aidl
index ebf6c05..25e8c4b 100644
--- a/gnss/aidl/android/hardware/gnss/gnss_assistance/GlonassAlmanac.aidl
+++ b/gnss/aidl/android/hardware/gnss/gnss_assistance/GlonassAlmanac.aidl
@@ -20,6 +20,8 @@
  * Contains Glonass almanac data.
  * This is defined in Glonass ICD v5.1, section 4.5.
  *
+ * If issueDateMs is -1, the GlonassAlmanac is not available.
+ *
  * @hide
  */
 @VintfStability
@@ -77,7 +79,10 @@
         double omega;
     }
 
-    /** Almanac issue date in milliseconds (UTC). */
+    /**
+     * Almanac issue date in milliseconds (UTC).
+     * If it is -1, the GlonassAlmanac is not available.
+     */
     long issueDateMs;
 
     /** Array of GlonassSatelliteAlmanac. */
diff --git a/gnss/aidl/android/hardware/gnss/gnss_assistance/GnssAlmanac.aidl b/gnss/aidl/android/hardware/gnss/gnss_assistance/GnssAlmanac.aidl
index f12378b..e03bbf0 100644
--- a/gnss/aidl/android/hardware/gnss/gnss_assistance/GnssAlmanac.aidl
+++ b/gnss/aidl/android/hardware/gnss/gnss_assistance/GnssAlmanac.aidl
@@ -24,6 +24,8 @@
  * For QZSS, this is defined in IS-QZSS-PNT section 4.1.2.6.
  * For Galileo, this is defined in Galileo-OS-SIS-ICD-v2.1 section 5.1.10.
  *
+ * If weekNumber is -1, the GnssAlmanac is not available.
+ *
  * @hide
  */
 @VintfStability
@@ -44,6 +46,7 @@
 
     /**
      * Almanac reference week number.
+     * If it is -1, the GnssAlmanac is not available.
      *
      * For GPS and QZSS, this is GPS week number (modulo 1024).
      * For Beidou, this is Baidou week number (modulo 8192).
diff --git a/gnss/aidl/android/hardware/gnss/gnss_assistance/KlobucharIonosphericModel.aidl b/gnss/aidl/android/hardware/gnss/gnss_assistance/KlobucharIonosphericModel.aidl
index e261e97..c1dba78 100644
--- a/gnss/aidl/android/hardware/gnss/gnss_assistance/KlobucharIonosphericModel.aidl
+++ b/gnss/aidl/android/hardware/gnss/gnss_assistance/KlobucharIonosphericModel.aidl
@@ -20,6 +20,8 @@
  * Contains Klobuchar ionospheric model coefficients used by GPS, BDS, QZSS.
  * This is defined in IS-GPS-200 20.3.3.5.1.7.
  *
+ * If all coefficients are 0, the KlobucharIonosphericModel is not available.
+ *
  * @hide
  */
 @VintfStability
diff --git a/gnss/aidl/android/hardware/gnss/gnss_assistance/LeapSecondsModel.aidl b/gnss/aidl/android/hardware/gnss/gnss_assistance/LeapSecondsModel.aidl
index 0ebd46d..d05fba8 100644
--- a/gnss/aidl/android/hardware/gnss/gnss_assistance/LeapSecondsModel.aidl
+++ b/gnss/aidl/android/hardware/gnss/gnss_assistance/LeapSecondsModel.aidl
@@ -20,11 +20,16 @@
  * Contains the leap seconds set of parameters needed for GNSS time.
  * This is defined in RINEX 3.05 "LEAP SECONDS" in table A2.
  *
+ * If leapSeconds is -1, the LeapSecondsModel is not available.
+ *
  * @hide
  */
 @VintfStability
 parcelable LeapSecondsModel {
-    /** Time difference due to leap seconds before the event in seconds. */
+    /**
+     * Time difference due to leap seconds before the event in seconds.
+     * If it is -1, the LeapSecondsModel is not available.
+     */
     int leapSeconds;
 
     /** Time difference due to leap seconds after the event in seconds. */
diff --git a/gnss/aidl/android/hardware/gnss/gnss_assistance/UtcModel.aidl b/gnss/aidl/android/hardware/gnss/gnss_assistance/UtcModel.aidl
index c16a711..2b291f0 100644
--- a/gnss/aidl/android/hardware/gnss/gnss_assistance/UtcModel.aidl
+++ b/gnss/aidl/android/hardware/gnss/gnss_assistance/UtcModel.aidl
@@ -20,6 +20,8 @@
  * Contains parameters to convert from current GNSS time to UTC time.
  * This is defined in RINEX 3.05 "TIME SYSTEM CORR" in table A5.
  *
+ * If weekNumber is -1, the UtcModel is not available.
+ *
  * @hide
  */
 @VintfStability
@@ -33,6 +35,6 @@
     /** Reference GNSS time of week in seconds. */
     int timeOfWeek;
 
-    /** Reference GNSS week number. */
+    /** Reference GNSS week number. If it is -1, the UTC model is not available. */
     int weekNumber;
 }