if not vs with the exception of

if not

adv

Used to link a semantically weaker word to a semantically stronger word following the adverb, both sharing the same basic meaning, indicating the increased likelihood of the former.

with the exception of

prep

With due allowance for (a specified detail); not including; other than.

How often have the words if not and with the exception of occurred in a corpus of books? (source: Google Ngram Viewer )