So, what I'll add tonight, as well as answering questions between now and Sunday, is the code to calculate (For any size) the difference between BigN and n for known RSA numbers. At that scale, you will see a Revelation. The difference is a VERY smooth number in every case.
Smooth numbers feature in the settings for a search in the general number field sieve.
Before this evening, have a look at large products, and the difference between n and BigN. The difference is the same as for n-1 and BigN-1, which you would find in [-f,1]