Tolerances are usually given as absolutes. I.e. No uncertainty. This is specified in by the American Society of Mechanical Engineers (ASME), although, it could probably be specified case to case. See this thread on the discussion https://www.eng-tips.com/viewthread.cfm?qid=176582. That thread references ASME Y14.5M-1994, section 2.5, Interpretation of Limits.
A newer version of that document is http://www-eng.lbl.gov/~shuman/NEXT/ANGEL2/ASME-Y14-5M-2004-Dimension-Ing-and-Tolerancing.pdf.