I (also) needed to know if the ADC continuous readings were overwritten or not...
This snippet of code was found in the ADC_Module::analog_init() function:
Code:
#ifdef ADC_TEENSY_4
    // overwrite old values if a new conversion ends
    atomic::setBitFlag(adc_regs.CFG, ADC_CFG_OVWREN);
    // this is the only option for Teensy 3.x and LC
    #endif