YOU SAID:

They would have never known if they had not done it

INTO JAPANESE

もし彼らがそれをしなければ、彼らは知らなかっただろう

BACK INTO ENGLISH

If they hadn't done it, they wouldn't have known.

INTO JAPANESE

もし彼らがそれをしていなかったら、彼らは知らなかっただろう。

BACK INTO ENGLISH

If they hadn't do it, they wouldn't have known.

INTO JAPANESE

彼らがそれをしなかったら、彼らは知らなかっただろう。

BACK INTO ENGLISH

If they hadn't done it, they wouldn't have known.

INTO JAPANESE

もし彼らがそれをしていなかったら、彼らは知らなかっただろう。

BACK INTO ENGLISH

If they hadn't do it, they wouldn't have known.

INTO JAPANESE

彼らがそれをしなかったら、彼らは知らなかっただろう。