I followed one of the example in The Rules of Unified English Braille Second Edition 2013 Section 8.8.1 page 88 on wether or not to use letter indicator before the word CDs. (NOT USED). But my proofreader told me that the letter indicator IS NEEDED in UEB codes. Please help me to clear up this confusing problem.
You are correct. CDs does not need the grade 1 symbol indicator because CD is not standing alone any more with the s after it (2.6). It does, however, require the capitals terminator before the s because the capital word indicator carries through letters unless it is explicitly stopped (8.4.1).
That said, CD's is the opposite. Now a grade 1 symbol (not word) (10.9.5) indicator is needed because CD is standing alone (2.6.4). The apostrophe stops capitals mode (8.4.2) so a capitals terminator is not needed.