Re: The Undertaker's clean loss record (Survivor Series 91-Present)
The Stone Cold low-blow at Summerslam 1998 is splitting hairs.
Look at the entire match, not just the ending. The referee relaxed the rules from the get-go; he let the two of them fight through the crowd for minutes without counting them out, for example.
The referee saw the low-blow (look at his mannerisms), but he chose not to disqualify Austin for it. Undertaker even handed the belt to Austin to acknowledge that he got beat.
I consider the Summerslam 1998 match a clean loss for Undertaker.