Volcanoes erupt around the world all the time. Bombs explode in the middle of wars. But you don't look out your window and automatically know that, do you?
The idea of a secretly launched or disguised launch craft is not implausible. If the government really wanted to make a secret ship launch, they could. Especially now, when dozens of craft launch and the general public just plain doesn't give a shit.
Launching a lander in the 1970's would require a Saturn V rocket, the most obnoxious fucking thing made by man. Also, we could only launch them from Kennedy Space Center in Florida.


That's like trying to sneak the entire US military through NYC without anybody finding out.