Regulation prohibiting revisiting of predicate factual determinations beyond three years in agency reopening proceeding does not prohibit revisiting such factual determinations in statutory direct appeals to the Board.
https://www.cadc.uscourts.gov/internet/opinions.nsf/5B15C6CE526BEB92852582BB00512041/$file/17-5098.pdf
Since 2011. An occasional commonplacing of the U.S. Circuit Courts of Appeal.
Neither an authoritative statement of the law nor legal advice. Quick work.