I spent so much time to figure out my mistakes(You can see it from my attempts :) ). You can save your time by checking theese tests. Hope they are helpful.

4
unknown
unknown
unknown
unknown

Answer: 1 2 4

2
unknown
unknown

Answer: 1 2


12
A
B
unknown
unknown
unknown
unknown
unknown
unknown
unknown
unknown
unknown
unknown

Answer: 12


4
A
B
C
D

Answer: 4

8
A
A
B
B
unknown
unknown
unknown
unknown

Answer: 4


6
A
A
B
B
unknown
unknown

Answer: 3

6
unknown
A
A
B
unknown
B

Answer: 2

6
A
unknown
unknown
A
unknown
unknown

Answer: 1

6
A
unknown
A
unknown
unknown
unknown

Answer: 1 2


4
A
A
A
B
Answer: Igor is wrong.

First and second tests are not correct.
"It is guaranteed that Igor could recognize the language of at least one of the phrases."

Some Others:
8
A
unknown
B
unknown
unknown
unknown
unknown
unknown

Answer: 4 8


10
unknown
unknown
unknown
A
unknown
unknown
unknown
unknown
B
unknown

Answer: 2 5 10


12
unknown
A
unknown
unknown
unknown
B
unknown
unknown
unknown
C
unknown
unknown

Answer: 3 4 6 12


12
unknown
A
unknown
unknown
unknown
B
unknown
D
unknown
C
unknown
unknown

Answer: 4 6 12


12
unknown
A
unknown
unknown
unknown
B
unknown
D
D
C
unknown
unknown

Answer: 4