You are right.
For KC868-A16
// Set i2c address for output
PCF8574 pcf8574_1(0x24); // channel 1-8 adress:100100
PCF8574 pcf8574_2(0x25); //channel 9-16 adress:100101
// Set i2c address for input
PCF8574 pcf8574_1(0x22); // channel 1-8 adress: 100010
PCF8574 pcf8574_2(0x21); //channel 9-16 adress: 100001
For KC868-A16
// Set i2c address for output
PCF8574 pcf8574_1(0x24); // channel 1-8 adress:100100
PCF8574 pcf8574_2(0x25); //channel 9-16 adress:100101
// Set i2c address for input
PCF8574 pcf8574_1(0x22); // channel 1-8 adress: 100010
PCF8574 pcf8574_2(0x21); //channel 9-16 adress: 100001