sindarin_grammar1-8  Exercise 2: The Past of padra-
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  i adan padrant     the man walked    (stem padra- + -nt)
  padrannen          I walked          (-nt becomes -nn- + the ending)

The summary says -nt turns into -nn- before a pronoun ending; the third
singular, with no ending, keeps -nt. Reconstructed (one learner's summary).
The other summary would give a different ending for "I".