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Any three could work depending on the project. I've actually used all 3 conditions in separate projects. The basement stairs are allowed to be narrower if they are not the primary exit (walk-out basement) or if they are existing and unchanged. Talk to the building inspector or code official to get their take on it. Sometimes they have unique solutions!
Suzie Van Cleave, AIA
4421 N Oakland Ave #200 O 414.204.8917
Milwaukee, WI 53211 C 847.778.1625