Full specifications are available. There is no security through obscurity here.
Actually, it is obscurity. The specification you linked to was NOT followed by the device manufacturer, they just assumed since they didn't tell anyone they violated a proper practice that no one would notice. The specifications listed by you requires devices to adhere to the random number generating requirements outlined in ISO 18031, which the machines did not. This standard mandates a unpredictable entropy source be used as the seed for any random number generating function. The devices were implementing the use of date and time as a seed. This is what a lot of kids are taught in school for computer class, but any cryptographer is supposed to avoid.
Just about every computer on the market today runs Unix, except the Mac (and nobody cares about it). -- Bill Joy 6/21/85