from collections import Counter
d = {'a': [4, 'Adam', 2], 'b': [3, 'John', 4], 'c': [4, 'Adam', 3], 'd': [4,
    'Bill', 3], 'e': [4, 'Bob'], 'f': [4, 'Joe'], 'g': [4, 'Bill']}
c = Counter([values[1] for values in d.values()])
c
Python count of items in a dictionary of lists