The early s905x4 boxes were released with ATV10 (kernel 4.9), so perhaps by the time Amlogic started manufacturing s905x4 rev 3/4 SOCs there was a SOC package change that is incompatible with the 4.9 kernel AML decoder module. And there was no need for them to address it because at that stage all new s905x4 boxes were being released with ATV11 (kernel 5.4)?