We generally solve queries in 24 hours but, sir was not well so could not solve queries of past few days, but it is expected that today onwards sir will be solving all queries in due time.

1st Point — if common partner situation exists on date of appointment then other firm is ineligible
2nd Point — if partner in charge who is certifying financial statements retires and joins other firm then such firm is also ineligible
Now if B retires before appointment then other firm is not covered in 1st point, if he joins back afterwards then also it wont be covered in 1st point as common partner situation should exist on date of appointment , which is not present in this case.
Bow we have to think from second point of view, if he is not partner in charge again no problem. But if he is partner in charge then 2 interpretations are possible.

1st — Literal interpretation — Other firm becomes ineligible if partner in charge joins it any time during 5 years of cooling — in present case he is not joining other firm , he was already partner there so no problem other firm is eligible.

2nd — Reasonable interpretation — other firm may not have common partner but if they have incharge partner then they should be ineligible  — from such interpretation other firm will get ineligible
you should write both such interpretation