lista = [
    [4, 'aa'],
    [4, 'bb'],
    [4, 'cc'],
    [4, 'dd'],
    [24, 'ee'],
    [24, 'ff'],
    [25, 'gg'],
    [25, 'hh'],
    [26, 'ii'],
    [26, 'jj'],
]

correta = []
num = []
for item in lista:
    if item[0] not in num:
        num.append(item[0])
        item.append(True)
        correta.append(item)
    else:
        item.append(False)
        # correta.append(item)

print(correta)
# [[4, 'aa', True], [24, 'ee', True], [25, 'gg', True], [26, 'ii', True]]

print(lista)
# [[4, 'aa', True],
#  [4, 'bb', False],
#  [4, 'cc', False],
#  [4, 'dd', False],
#  [24, 'ee', True],
#  [24, 'ff', False],
#  [25, 'gg', True],
#  [25, 'hh', False],
#  [26, 'ii', True],
#  [26, 'jj', False]]