I was surprised just now not to find "Philip Melancthon", as he is often called, in the Factbook. No wonder his letter to fellow Reformer Martin Bucer in LLS:RGLTRLNGRF, which uses that spelling, merely appears in Bucer's Factbook article as being from the book in question, rather than the person. Unfortunately, searching for Melancthon in the Factbook curiously fails to find the entry Philipp Melanchthon, but that should be any easy fix.
(Meanwhile, the same fate has befallen the two letters from Peter Martyr Vermigli to Martin Bucer, even though Peter Martyr Vermigli has two Factbook articles devoted to him.)
At any rate, LLS:RGLTRLNGRF inspires me to recommend Factbook articles for everyone else in that volume who is thought important enough to be found within, but not important enough to have a Factbook article yet--like Jane Seymour, whose death alone presently appears in the Factbook.