In establishing continuity with House of Frankenstein, the resurrection of Frankenstein is a well-treated plot element, but it is never explained how Baron Latos and Larry Talbot have come back from their deaths in that movie.
The skeleton of Dr. Niemann in the cave has a highly visible, perfectly even, horizontal seam line running all the way around the top of the head; it is obviously a skeleton model often sold by medical and education supply houses to schools, etc.
Although the Frankenstein Monster has been mouldering in a warm, moist environment for years (in the muddy caves at the base of the cliff), his clothing is apparently immortal, too, for in the very next scene after his discovery in the caves his clothing appears pristine and brand new, showing no signs of the inevitable mold and rot that ordinary fabric would incur in such conditions (unless, of course, the Doctor has re-dressed him in identical clothes, which seems unlikely). In contrast, the clothing of Dr. Niemann, who was buried/and found with the Monster, has completely rotted away, to reveal only bones.
The goof item below may give away important plot points.
When the blood of Dracula has overtaken Dr. Edlemann, we see his reflection in the mirror disappear. However, later in the film, as the doctor leads Larry Talbot out into the garden as the full moon rises, we see his reflection in the window.