Thread:ADour/@comment-30536711-20160811205959/@comment-4651179-20160811222153

I found the source to that claim, in Ultimate Doom #3, Sue refers to Reed's base of operation (revealed to be the Negative Zone in issue #4) this way in the following line: "like we thought, he found himself a pocket dimension, set up shop, and has been launching these organic biotech attacks from there."

The dialogue implies that the Negative Zone was known only to Reed at the time, unlike the N-Zone, whose existence was known by authorities.