428 Cobra Jet Harmonic Balancer C8AZ-6316-B - Why two versions A1 and A2 ?

[6s1640]

On the Mustang 428 Cobra Jet site, they show two version of the 428 Cobra Jet harmonic balancer.  "...The A2 damper is slightly heavier (6.9 lbs. vs. 6.3 lbs.) and has a thicker (0.75" vs. 0.55") outer ring as compared to the A1 damper. They both have the same 7" outside diameter..."  Can anyone help me understand why Ford engineered two versions under the same part number C8AZ-6316-B?  The CJ site has received input from 428 CJ owners, claiming both A1 and A2 balancers have been found on the 68 Cobra Jet cars.  Are they both equally right?

I checked on the Ford MPC, and it provides no additional information for the two versions, both the June 1968 and May 1975 printing.  The 1975 MPC shows D2TZ-6316-A.

Thanks

Cory