I believe this is what you've attempted to do based on the example you showed me above:
Code:
on $*:text:/^\.(19[89][0-9]|200[0-9]|201[0-3])\.(.+\056){3}.+\-$/iS:#some-channel:{
if ($regml(1) isnum 1980-1990) { write file1.txt ... }
elseif ($regml(1) isnum 1991-1999) { write file2.txt ... }
elseif ($regml(1) isnum 2000-2009) { write file3.txt ... }
elseif ($regml(1) isnum 2010-2013) { write file4.txt ... }
}