In the “old” library repo, there is a wiki page https://github.com/KiCad/kicad-library/wiki/Status-of-the-libraries
I don’t know how that table was produced, I guess there is not an up to date one. For curiosity, I hacked the Travis script to produce an updated version. The score is not a percentage, but a weighted index such that 100 = no errors, 0 means an average of 5 errors per symbol. Generally the score is above 80, which is pretty good!
Library Symbols Score
--------------------------------------------------------
Amplifier_Audio 49 98
Amplifier_Buffer 5 100
Amplifier_Current 31 99
Amplifier_Difference 3 100
Amplifier_Instrumentation 12 100
Amplifier_Operational 54 97
Amplifier_Video 2 100
Analog 7 100
Analog_ADC 52 94
Analog_DAC 51 93
Analog_Switch 57 100
Audio 31 97
Battery_Management 34 84
Comparator 13 95
Connector_Generic 318 100
Connector_Generic_Shielded 238 67
Connector_Specialized 117 5
Converter_DCDC 2 80
CPLD_Altera 25 100
CPLD_Xilinx 13 92
CPU 1 80
Device 342 64
Diode 32 26
Diode_Bridge 11 96
Diode_Laser 3 100
Display_Character 75 100
Display_Graphic 13 82
Driver_Display 7 83
Driver_FET 33 98
Driver_LED 27 84
Driver_Motor 31 88
Driver_Relay 3 93
DSP_Freescale 1 100
DSP_Microchip_DSPIC33 11 98
DSP_Texas 1 100
FPGA_Actel 18 17
FPGA_Xilinx 30 0
FPGA_Xilinx_Artix7 27 40
FPGA_Xilinx_Kintex7 18 40
FPGA_Xilinx_Spartan6 45 40
FPGA_Xilinx_Virtex5 41 40
FPGA_Xilinx_Virtex6 28 40
FPGA_Xilinx_Virtex7 31 38
Graphic 29 100
Interface 19 95
Interface_CAN_LIN 34 94
Interface_CurrentLoop 1 100
Interface_Ethernet 8 92
Interface_Expansion 19 98
Interface_HID 4 100
Interface_LineDriver 10 100
Interface_Optical 11 100
Interface_Telecom 2 100
Interface_UART 29 92
Interface_USB 42 88
Isolator 68 100
Isolator_Analog 3 100
Jumper 9 51
LED 31 86
Logic_74xgxx 68 0
Logic_74xx 138 90
Logic_CMOS_4000 38 73
Logic_CMOS_IEEE 91 0
Logic_LevelTranslator 10 100
Logic_Programmable 6 77
Logic_TTL_IEEE 147 0
MCU_AnalogDevices 1 100
MCU_Atmel_8051 4 0
MCU_Atmel_ATMEGA 112 0
MCU_Atmel_ATTINY 74 0
MCU_Atmel_AVR 23 0
MCU_Cypress 3 53
MCU_Infineon 2 60
MCU_Intel 8 72
MCU_Microchip_PIC10 12 93
MCU_Microchip_PIC12 30 100
MCU_Microchip_PIC16 110 86
MCU_Microchip_PIC18 41 95
MCU_Microchip_PIC24 1 100
MCU_Microchip_PIC32 3 100
MCU_Microchip_SAME 3 100
MCU_Microchip_SAML 6 90
MCU_Module 10 96
MCU_NXP_HC11 2 0
MCU_NXP_Kinetis 66 92
MCU_NXP_LPC 15 96
MCU_NXP_S08 58 97
MCU_Parallax 3 93
MCU_SiFive 1 80
MCU_SiliconLabs 3 100
MCU_ST_STM32 464 80
MCU_ST_STM8 7 100
MCU_Texas 5 0
MCU_Texas_MSP430 121 0
Mechanical 6 73
Memory_Controller 1 100
Memory_EEPROM 30 100
Memory_EPROM 9 100
Memory_Flash 14 0
Memory_NVRAM 6 87
Memory_RAM 35 0
Memory_ROM 5 0
Memory_UniqueID 2 80
Motor 13 100
Oscillator 30 81
Potentiometer_Digital 16 68
power 93 99
Power_Management 43 62
Power_Protection 27 100
Power_Supervisor 13 46
pspice 11 20
Reference_Current 5 100
Reference_Voltage 45 86
Regulator_Controller 19 98
Regulator_Current 1 100
Regulator_Linear 159 98
Regulator_SwitchedCapacitor 10 96
Regulator_Switching 163 93
Relay 50 99
Relay_SolidState 16 100
RF 12 90
RF_AM_FM 8 98
RF_Bluetooth 12 95
RF_GPS 1 100
RF_Mixer 1 80
RF_Module 2 100
RF_RFID 1 100
RF_WiFi 4 95
RF_ZigBee 2 90
Sensor 6 90
Sensor_Audio 1 80
Sensor_Current 28 86
Sensor_Gas 1 100
Sensor_Humidity 3 87
Sensor_Magnetic 9 98
Sensor_Motion 16 91
Sensor_MultiFunction 2 30
Sensor_Optical 32 87
Sensor_Pressure 5 92
Sensor_Proximity 13 98
Sensor_Temperature 39 81
Sensor_Touch 9 87
Sensor_Voltage 1 100
Switch 49 84
Timer 13 100
Timer_RTC 7 37
Transformer 44 82
Transistor_Array 4 0
Transistor_BJT 157 65
Transistor_FET 27 76
Transistor_IGBT 1 100
Triac_Thyristor 4 0
Valve 14 16
Video 26 0