This applies to All Interfaces

Pro-Tools Artist is limited to 32 audio tracks, 32 aux channels, 32 instrument tracks, 64 MIDI tracks, and 16 channels of I/O. This means that in the Pro-Tools Artist I/O, you will be able to see all of your device's inputs, however, only the first 16 inputs will record into Pro-Tools Artist but you can have 32 audio tracks. 

Below is an example of a Clarett 8Pre USB. In Pro-Tools there are 20 audio tracks however only the first 16 inputs can be used to record audio. 

You would be able to use:

• Analogue Inputs 1-8 
• SPDIF Inputs 1-2 (9-10)
• ADAT Inputs 1-6 (11-16)
• ADAT inputs 7-8 will not record into Pro-Tools Artist