Parallel routs on a 12-string headstock

[adam_swapp]

It was noted in another thread that parallel routs on the headstock of a 360-12 are indicative of an early model. Does this apply to the 330-12 as well? How rare is it to find a guitar with the parallel routs? What year(s) would you expect to find those? How much of a premium is one of these early models worth? And finally, it seems like this might be an easy way (certainly easier than curved routs) to do a 6 to 12 conversion. Aside from the obvious (like bare wood in the routs), any suggestions on authenticating such a guitar?

Thanks.