Heck, the proof of that was the fact that they never grounded the 747 lineup.
That got pointed out so often back then.
They didn't ground 777s after the Malaysian Airlines flight disappeared. Or the MD-11s after the Swissair crash in 1998. Or Airbus 300s after American Airlines Flight 587 in 2001. Or 767s after Lauda Air Flight 004 in 1991. Or Airbus 340s after the Air France Flight 447 in 2009. They ground an airplane only after they identify a cause and only if it represents a possible immediate danger to similar aircraft. Otherwise they specify a fix and set a deadline for implementing it.