Table:
0
A
B
C
D
E
1
District
Vacator
Reason for change
Successor
Date successor seated
2
Pennsylvania 18th
Robert J. Corbett (R)
Died April 25, 1971
H. John Heinz III (R)
November 2, 1971
3
Kentucky 6th
John C. Watts (D)
Died September 24, 1971
William P. Curlin, Jr. (D)
December 4, 1971
4
Pennsylvania 27th
James G. Fulton (R)
Died October 6, 1971
William S. Conover (R)
April 25, 1972
5
Alabama 3rd
George W. Andrews (D)
Died December 25, 1971
Elizabeth B. Andrews (D)
April 4, 1972
6
New York 20th
William Fitts Ryan (D)
Died September 17, 1972.
Vacant
Not filled this congress
7
Ohio 16th
Frank T. Bow (R)
Died November 13, 1972.
Vacant
Not filled this congress

Questions and formulas:
Question: How many successors were seated in the New York 20th district?
Formula: ROWS(UNIQUE(FILTER(D1, A1="New York 20th")))
Formula2: ROWS(UNIQUE(FILTER(D2:D7, A2:A7="New York 20th")))
Level: medium