Hi Laurie. You are correct -- Nemeth stays in effect until you close it with a Nemeth Code terminator. A page change (print or braille) does not terminate Nemeth Code.
The "Guidance" does state that neither indicator should be separated from what it applies to (point 11 on page 11). In other words, don't end a page (print or braille) with an opening Nemeth Code indicator, and don't start a page (print or braille) with a Nemeth Code terminator.