Solution
This is because there is a digital signal processing (DSP) chain in front of the ADC RX resolution. During various digital/mathematical operations, the bit width is expanded.
The ADC still provides output at 14-bit resolution, but LabVIEW receives it as 16 bits. This bit expansion occurs during digital/mathematical operations. The NI DSP library uses <+/-, 18,1>, meaning the total fixed-point (FXP) word is 18 bits, and the data is reported to the host as 16 bits.