I suppose Rockefeller was too petrified to use a typewriter to write this note. ;-)
Possibilities:
1) He never sent the letter.
2) He Just wrote it a few days ago.
3) He sent it, but made no effort to make sure it got special notice. If this last scenario is accurate, it was plotted 2-3 years in advance.
Any could be true.
What is key, though, is that Roberts states Rockefeller praised the program only two weeks ago. That nukes the letter, real, plotted or imagined.
"I suppose Rockefeller was too petrified to use a typewriter to write this note"
HAH! He was worried that we'd check the font!