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Jr., Sr., III

Jr. and Sr. are preceded and followed by comma in full name:
            John M. Fahey, Jr. (left), went to. . .
but     John Jr. hurried. . . .

No commas with Roman numeral attached to name:
            Nicholas DeVore III arrived.

For possessive add apostrophe plus s:
            John M. Fahey, Jr.'s memo
            Joel Bourne III's picture.