When you record MIDI, you can specify which MIDI input each recording MIDI track should use. However, you can also record any MIDI data from any MIDI input. For this to work, you must first set up which inputs are included when you select All MIDI Inputs for a MIDI track.
Procedure
Result
When you select All MIDI Inputs on the Input Routing pop-up menu of a MIDI track in the Routing section of the Inspector, the MIDI track uses all MIDI inputs that you specified in the MIDI Port Setup.