The kernel version is a value not a field.

You're welcome to assume forever that there will be a version field, if it ever becomes the case that this simply makes no sense anymore then a sensible dummy value will be placed in[0]

[0] - http://lkml.iu.edu/hypermail/linux/kernel/1710.3/02487.html

    "There's a number of fields in /proc/<pid>/stat that are printed out as zeroes, simply because they don't even *exist* in
    the kernel any more, or because showing them was a mistake (typically an information leak). But the numbers got replaced
    by zeroes, so that the code that used to parse the fields still works."