diff --git a/keyboards/bastardkb/charybdis/3x5/3x5.c b/keyboards/bastardkb/charybdis/3x5/3x5.c
index d896cf692399..8d9e625ae4dd 100644
--- a/keyboards/bastardkb/charybdis/3x5/3x5.c
+++ b/keyboards/bastardkb/charybdis/3x5/3x5.c
@@ -33,6 +33,10 @@
  * ╰────────────────────╯                 ╰────────────────────╯
  *                   15  16  17     33  34  XX
  *                 ╰────────────╯ ╰────────────╯
+ *
+ * Note: the LED config simulates 36 LEDs instead of the actual 35 to prevent
+ * confusion when testing LEDs during assembly when handedness is not set
+ * correctly.  Those fake LEDs are bound to the physical bottom-left corner.
  */
 led_config_t g_led_config = { {
     /* Key Matrix to LED index. */
@@ -61,7 +65,7 @@ led_config_t g_led_config = { {
     /* index=24 */ { 188,  42 }, { 188,  21 }, { 188,   0 },
     /* index=27 */ { 170,   0 }, { 170,  21 }, { 170,  42 },
     /* index=30 */ { 152,   0 }, { 152,  21 }, { 152,  42 },
-    /* index=33 */ { 152,  64 }, { 134,  64 },
+    /* index=33 */ { 134,  64 }, { 152,  64 }, {   0,   0 },
 }, {
     /* LED index to flag. */
     // Left split.
@@ -77,7 +81,7 @@ led_config_t g_led_config = { {
     /* index=24 */ LED_FLAG_KEYLIGHT, LED_FLAG_KEYLIGHT, LED_FLAG_KEYLIGHT,
     /* index=27 */ LED_FLAG_KEYLIGHT, LED_FLAG_KEYLIGHT, LED_FLAG_KEYLIGHT,
     /* index=30 */ LED_FLAG_KEYLIGHT, LED_FLAG_KEYLIGHT, LED_FLAG_KEYLIGHT,
-    /* index=33 */ LED_FLAG_KEYLIGHT, LED_FLAG_KEYLIGHT, // Thumb cluster
+    /* index=33 */ LED_FLAG_KEYLIGHT, LED_FLAG_KEYLIGHT, LED_FLAG_KEYLIGHT, // Thumb cluster
 } };
 #endif
 // clang-format on
diff --git a/keyboards/bastardkb/charybdis/3x5/config.h b/keyboards/bastardkb/charybdis/3x5/config.h
index 5bf048c82969..ffa8b68d05f1 100644
--- a/keyboards/bastardkb/charybdis/3x5/config.h
+++ b/keyboards/bastardkb/charybdis/3x5/config.h
@@ -40,9 +40,9 @@
 #define ROTATIONAL_TRANSFORM_ANGLE -25
 
 /* RGB settings. */
-#define RGBLED_NUM 35
+#define RGBLED_NUM 36
 #define RGBLED_SPLIT \
-    { 18, 17 }
+    { 18, 18 }
 
 /* RGB matrix support. */
 #ifdef RGB_MATRIX_ENABLE
diff --git a/keyboards/bastardkb/charybdis/4x6/4x6.c b/keyboards/bastardkb/charybdis/4x6/4x6.c
index 6cd8fffee7b8..85e8b5fdd16f 100644
--- a/keyboards/bastardkb/charybdis/4x6/4x6.c
+++ b/keyboards/bastardkb/charybdis/4x6/4x6.c
@@ -36,6 +36,10 @@
  *                       26  27  28     53  54  XX
  *                           25  24     55  XX
  *                     ╰────────────╯ ╰────────────╯
+ *
+ * Note: the LED config simulates 58 LEDs instead of the actual 56 to prevent
+ * confusion when testing LEDs during assembly when handedness is not set
+ * correctly.  Those fake LEDs are bound to the physical bottom-left corner.
  */
 led_config_t g_led_config = { {
     /* Key Matrix to LED index. */
@@ -70,6 +74,7 @@ led_config_t g_led_config = { {
     /* index=45 */ { 160,   0 }, { 160,  12 }, { 160,  24 }, { 160,  36 },
     /* index=49 */ { 144,   0 }, { 144,  12 }, { 144,  24 }, { 144,  36 },
     /* index=53 */ { 112,  52 }, { 128,  64 }, { 112,  64 },
+    /* index=56 */ {   0,   0 }, {   0,   0 },
 }, {
     /* LED index to flag. */
     // Left split.
@@ -89,6 +94,7 @@ led_config_t g_led_config = { {
     /* index=45 */ LED_FLAG_KEYLIGHT, LED_FLAG_KEYLIGHT, LED_FLAG_KEYLIGHT, LED_FLAG_KEYLIGHT,
     /* index=49 */ LED_FLAG_KEYLIGHT, LED_FLAG_KEYLIGHT, LED_FLAG_KEYLIGHT, LED_FLAG_KEYLIGHT,
     /* index=53 */ LED_FLAG_KEYLIGHT, LED_FLAG_KEYLIGHT, LED_FLAG_KEYLIGHT, // Thumb cluster
+    /* index=55 */ LED_FLAG_MODIFIER, LED_FLAG_MODIFIER,                    // Thumb cluster fakes
 } };
 #endif
 // clang-format on
diff --git a/keyboards/bastardkb/charybdis/4x6/config.h b/keyboards/bastardkb/charybdis/4x6/config.h
index 75b93f0e439c..b2efa19d3622 100644
--- a/keyboards/bastardkb/charybdis/4x6/config.h
+++ b/keyboards/bastardkb/charybdis/4x6/config.h
@@ -40,9 +40,9 @@
 #define ROTATIONAL_TRANSFORM_ANGLE -25
 
 /* RGB settings. */
-#define RGBLED_NUM 56
+#define RGBLED_NUM 58
 #define RGBLED_SPLIT \
-    { 29, 27 }
+    { 29, 29 }
 
 /* RGB matrix support. */
 #ifdef RGB_MATRIX_ENABLE