I'm not an expert in that device but my understanding of the data sheet is that there is more than one PWM module and they have different base addresses. The offset is the difference in address of the register from the applicable PWM module base address.
For example:
PWM0 base: 0x4002.8000 + 0x00C gives the PWMINVERT register address for PWM0 module
PWM1 base: 0x4002.9000 + 0x00C gives the PWMINVERT register address for PWM1 module