The selected items are editable (for example because "Avoid automatically setting MIDI items from other tracks editable" is OFF)
There are selected notes across multiple items
Then articulation insertion should apply to all MIDI items with selected notes simultaneously, with the same logic currently used for insertion when multiple tracks are selected.
When these conditions are true:
Then articulation insertion should apply to all MIDI items with selected notes simultaneously, with the same logic currently used for insertion when multiple tracks are selected.
More discussion here