@if(@_jscript) <-- this JScript CC recognised by IE9
newIN = document.createElement("<input name='"+nam+"'>"); <-- this JScript invalid in IE9
So you have to implement another JScript conditional comment to test specifically for IE9 because IE9 doesn't support that one JScript statement that you can't use feature sensing to detect.
CC as implemented by Microsoft are are almost useless because they didn't implement them consistently. The one instance where a CC is needed in JScript is broken in IE9 because that's the one part of JScript that IE9 doesn't support.