And even if the NCR doesn't pose a threat to Nelson that doesn't mean they can take Forlorn without the magical courier. How would they? They can't go by I-95 because they don't hold Novac. They can't go through the valley because they'd be sniped to death. The ONLY way to get Forlorn hope is to take Novac.
Ayup. You'd think nobody'd ever heard of basic military flanking tactics, which is what a Cottonwood to Novac thrust would be. I saw that plain as day, on the first playthrough. Cut off their main supply route, roll up the small outposts defending that corner, pincer the NCR roadblock between Novac and Nelson, and watch them all scramble in confusion. It would be any defending general's nightmare. With enough troops pushed into a Novac thrust, the NCR at Forlorn Hope and the Dam would be very close to being surrounded, and be forced to withdraw. It would be more than worth sacrificing whatever recruits it took to take out or blow past the sniper post at Echo, to break out of Cottonwood Cove- I don't see Caesar or Lanius having any qualms with that kind of operation. Once a force reached the top of the ridge near Searchlight, they would easily be able to hook around and outflank Echo, and make that camp untenable. The southern flank is the NCR's weakest and poorest-defended sector, and Caesar would be negligent not to exploit it.