As I understand, the first ~300-400 cars had cast or sintered arms, all of which were recalled. These and about 1000 more thereafter have the billet arms after which they switched to a forged process. While the cast arms should have all been replaced by now, one should consider that during the later switch from billet to forged, maybe some cars have mixed arms (late 2005)?
I recall media reports that the recall replacement process was executed by dedicated travelling GT teams that tracked down the few hundred cars in circulation at the time. My car, 2005 #0604 built 10/29/04 (described as #212 of 2022) was one recalled, and according to the Oasis report, had the arms replaced on 4/4/05 apparently by the dealer while under his ownership. Maybe these travelling specialists did not reach all of the cars?