i guess that for otter is a misprint in the source and should read evidence for this is that where silverman describes the normal outcome of tapping with distinction marked by length contrast on the preceding vowel we read vtv v v silverman p also this is consistent with how the length contrast on the preceding vowel is marked in other surroundings e g in the cited table in knot with regard to nod i think there is nothing wrong it is pretty much the point of silverman's article that in this particular position de voicing is common of course additional sources would be nice