Looking on the internet deeply has found these results:

if not is the most popular phrase on the web.

if not so 180,800 results on the web	if not 1336,000,000 results on the web More popular!
Some examples and use cases from the internet:	Some examples and use cases from the internet:
Oct 28, 2014 ... Metro Jul 9, 2014 ... This lightly refers to my food being close to the best value through the "if not". So the use of "if not" allows one to compare values with an�... Hola. �Me ayud�is con esta frase? Not all those women were malleable;in fact, some were as steely as their male counterparts, if not so. North crashes 'almost a comedy of errors if not so tragic', senator says. New York senator piles on scathing report by NTSB, which says�... ;and if not so, thereafter thou shalt cut it off.' Parallel Commentaries. Matthew Henry's Concise Commentary 13:6 9 This parable�... and if indeed it may bear fruit	It doesn't look like this phrase is very popular! The search could not find any examples on the internet.

if not so

180,800 results on the web

if not

1336,000,000 results on the web

More popular!

Oct 28, 2014 ... Metro
Jul 9, 2014 ... This lightly refers to my food being close to the best value through the "if not". So the use of "if not" allows one to compare values with an�...
Hola. �Me ayud�is con esta frase? Not all those women were malleable;in fact, some were as steely as their male counterparts, if not so.
North crashes 'almost a comedy of errors if not so tragic', senator says. New York senator piles on scathing report by NTSB, which says�...
;and if not so, thereafter thou shalt cut it off.' Parallel Commentaries. Matthew Henry's Concise Commentary 13:6
9 This parable�...
and if indeed it may bear fruit

It doesn't look like this phrase is very popular! The search could not find any examples on the internet.