I have read in one version that Arjun went to heaven and received all the Divya astras from Devs. Now, if Arjun had all the Divya astras, why could he not counter:
1. Bhargav astra shot by Karna.
2. Nagastra shot by Karna. ( Krishna made the chariot sink in ground to save Arjun ).
3. Naryan astra shot by Ashwattama.
4. In some versions, Karna shoots Vaisnav astra which Arjun could not counter so Krishna had to stop it.