[had done so] [had done it], [had done] or [had had]

I have made up the sentences below.

(1) Jack, who is a hockey player, had a serious leg injury last December. He hasn't played since then. In his previous season, he didn't score as many goals as he had done so before.

(2) .... In his previous season, he didn't score as many goals as he had done it before.

(3) .... In his previous season, he didn't score as many goals as he had done before.

(4) .... In his previous season, he didn't score as many goals as he had had before.

I am not sure which one makes sense. Most of my non-native English speaking friends think (3) is correct. Please help me. Thank you very much for your help.