Possible Clues:

• Ended incrementally, with 'out'
• Disconcerted in recital, but not all at once
• Stopped gradually, with "out"
• Introduced in stages
• With 107-Across, discontinued gradually
• In the auditorium, unsettled by stages
• Disconcerted by audition being spread over stages
• Fourth stage perhaps said to have surprised
• Gradually introduced, with 'in'
• Introduced in stages, with "in"