Disqualified Auditor

in companies act, if director is disqualified and was previously appointed by mistake then also, his work is valid and he is liable...

but are there similar provisions for auditor who has issued annual report for 3 years and came to know that he was disqualified all of the years.. is work already done by him valid..??
main point : the auditor was disqualified right from his appointment but was not knowing the same and has done work in good faith in all 3 years... but now he came to know about his disqualification...
what is validity of his work?? remaking of all annual reports???