Thanks for sending the print pages. First, I do not think that the letters themselves are displayed because there is no surrounding text. From the print pages you sent, the letters themselves ARE the text. So, do not treat the letters as displayed. These letters are a series of blocked paragraphs, with some occasional indented paragraphs within the body of the letter. Since the closings for all the letters is at the left margin, these are not treated as an attribution, but simply as very short blocked paragraphs. Each closing is on the same print page as its associated letter, so there is no issue with page change indicators.
If the closing falls on the next BRAILLE page, I would treat it as any other blocked paragraph that starts on a new braille page. Since the closing is NOT an attribution, the guidelines for attributions do not apply. Consider also that the text of the letters is clear and consistent, and the meaning should be clear to the reader as the text is read.