Back in 1986, I don't think the NRA had anything near the communications network it has now. Even if the NRA had immediately mobilized to stop the FOPA as soon as the machine-gun ban was added to it, what would it have been able to do before the amended bill was passed?
How much time elapsed between the voice vote on the amendment and the bill's signing into law? Even if the NRA had sent out postcards on the day after the machine-gun garbage was added to the bill, would people have actually received them before the bill was signed?
The Lautenberg Abomination was much less forgivable. The GOA had no trouble finding out about the bill before it passed, and there is plenty of stuff in the Lautenberg Abomination that can be opposed without being branded a zealot (e.g. the fact that a person's RKBA can be denied indefinitely without so much as an allegation--much less evidence--that they've done anything criminal). I found the NRA's silence on the Lautenberg Abomination puzzling and alarming.