Actually it is proven. If you search up some YouTube videos on people glitch in through walls and getting into closed areas you'll see completely rendered environment and most areas are plagued with enemies and even bosses. I know one I saw looks like reksis/archon dude or whatever his name is from the warp drive mission on earth. These places have been cut this much I know. Places left for speculation are Venus and Mars. On Venus there is a chamber with a column of light guarded by enemies. Next is Mars on black garden mission. Right after you defeat the divisive mind instead of running toward the heart head the other path and look right. Big wall of light that repulses you every attempt to enter. Lastly I found something odd on earth. Head to the forgotten shore on earth and enter the building by the shore. Head down and there is hive majors/ultras in which one is rather difficult and is even adorned with a fancy name. Not just chosen knight or hollowed knight. I digress. It's proven even if some refuse to see the facts in front of them.