The late C style earcups that I have seen on ebay lack the lip. I won't buy them and go through all the work of sewing them into a helmet unless they are accurate. I don't think anybody would. I also can't fathom somebody going through the gyrations of making a reproduction earcup and then make them inaccurately.
If you (or anybody else) know of somebody that makes a repro earcup that is accurate (includes the lip), please tell me how to contact him (or her).