Unresolved initials and doubtful abbreviation

Meaning

The supplied transcription marks B[r?] as uncertain; the note proposes Bruder only as a plausible expansion. The brackets and question mark are therefore information about the reading, not decorative punctuation to remove. B. T. at the close of the Second Response and the longer initialled signature of the First Response are likewise not expanded here.

An unexplained abbreviation can still have a clear local function: title, address, closing siglum or signature. Explaining that function is more responsible than supplying a personal name unsupported by the text. The lexicon distinguishes those functions and preserves the supplied uncertainty without claiming a fresh examination of the original letters.