(a) That's wrong. It often happens that performance appears to be correct and complete, but the goods supplied (or work done) suffers from a hidden defect that only becomes apparent after some time, or after being used. Since the defects are hidden, there is no discernable reason to reject the performance when it is made, and so the buyer initially accepts the seller's performance.
But that is not the end of the matter. If it can be shown that the defects complained of were present at the time of delivery or when the work was done, (for example, that the computerised components in the washing machines were faulty when delivered) then the seller will be in breach of contract. If the defect is sufficiently serious, the buyer will be entitled to reject the goods and claim damages for any loss or, for less serious defects, at least claim damages.
This right exists even though the goods were initially received and used until the defect was discovered.