Cessna wingspar AD - why not 421?

Received this article in my email today from AOPA. An update on the
Cessna wingspar AD. I am curious why the 421 isn't included in this
list of aircraft. I thought all the 4 series shared a common wing?

Glad to see the 3 series are not included (yet)!

-Nathan



FAA GRANTS MEETINGS FOR TWIN CESSNA OWNERS
Owners of twin-engine Cessna airplanes will be allowed to voice their
concerns in public meetings over proposed airworthiness directives
(ADs),
the FAA announced. Believing that the ADs are based entirely on theory
and
have no real-world data to back them up, AOPA lobbied hard for the
meetings.
The FAA has refused to reveal any data that may support safety issues.
The
ADs would require owners of Cessna models 401, 401A, 401B, 402, 402A,
402B,
402C, 411, 411A, and 414A to install an expensive spar strap
modification,
and perform repetitive spar inspections. AOPA estimates the cost of
compliance to be $70,000 per aircraft, more than many of these models
are
worth. The meetings will take place on March 3 and 4 at a hotel near
Washington Dulles International Airport, just outside Washington, D.C.
AOPA urges owners to either attend the meetings or file formal
comments
before the extended comment period ends on April 5. Click here to
download
more information ( http://download.aopa.org/epilot/2004/2002ce57ad.pdf
)