This subject has been kicked around for years. As far as I know, no definitive answer has come forth. I agree with Pat, generally. However, I feel the Gau-marked examples are likely period. Those so marked generally have characteristics in common. I would not pass on an M36 because of Gau marks alone. As noted, they are mostly, if not exclusively, found on daggers with "Type I" chains. The same holds true for the crossguards being marked "PA" internally and the original finish being blued ("anodized"). It may be some Gau leader or other big wig wanted them with Gau marks, for reasons of his own. The marks tend to be on early M36 examples. I don't have the statistics, but I think only certain Gau marks appear on them. I know of no presumedly authentic M33 SS dagger with Gau marks.