I know they didn't go home until they finished that task.语法正确吗?

I know they didn't go home until they finished that task.语法正确吗?
I know they didn't go home until they finished that task.语法正确吗?

I know they didn't go home until they finished that task.语法正确吗?
I know they didn't go home until they finished that task.语法正确吗?
答：语法正确.
译：我知道,他们直到完成了那项工作才回家.
析：I know是主句,后跟宾语从句,表示知道了一个事实（过去发生的）,省略了连词that
当主句为现在时态时,从句根据实际情况可以是任何时态的句子.不涉及时态一致的问题.只要考虑这个从句就可以了.
not ...until...表示“直到.才.” until可以跟一过去时间,也可以跟一个从句,表示过去某个时刻.主句的动作应为可延续的动词,如worked,lived,etc.但是短暂性动词的否定式表示的不是动作,而是一种状态（情况）,也是可以延续的.表示这种状态一直延续到until所表示的那个时间为止.

正确 过去时也用了

对！

I know they won't go home until they finished that task.更合适一些.

I know they didn't go home until they finished that task.
I know they would go home til they finished that task.
都一样，都对。

是正确的，在描述过去的事。