"They never said they were perfect". Very true. And yet, as we know, the loyal jw is expected to treat the "spiritual food" as though it comes from God, which implies that it is perfect.
Until that jw notices that a mistake was made - a missed date for Armageddon perhaps. Or, he is informed that there is a change in "understanding" of a teaching.
Then, it's "they never said they were perfect".
In the meantime, it is implied, or even directly stated, that the fault lies with the average jw, who harbored "expectations" that turned out to be unrealistic, even though the expectations were created by Watchtower teachings.