Oh, Dickens was fine, wwh. Here's several definitions from MW, including one that indicates herald and harbinger may be used synonymously:

"2 a : an official crier or messenger having duties similar in one or more respects to those of the herald of medieval and modern Europe <Mercury was the gods' herald> b : one (as a soldier) who signals with a trumpet <more chieftains came, with heralds who blew on trumpets that were twelve feet long -- Hector Bolitho> c : AVANT-COURIER
3 a : one that precedes or foreshadows : HARBINGER, FORERUNNER <flights of ravens ... are the sure heralds of the approach of the deer -- Farley Mowat> <revolutions ... were the heralds of social changes -- R.W.Livingstone> b (1) : one that conveys news or proclaims : ANNOUNCER <hark the herald angels sing -- George Whitefield> <it was the lark, the herald of the morn -- Shakespeare> (2) : one that supports or advocates : SPOKESMAN <conspicuous herald of this enfranchising movement -- C.A.Dinsmore>"