In Through the Looking Glass, Alice became her own mirror self. Count Dracula, however, has no mirror self. Early on, Harker notes the lack of mirrors in the Count's home; later, he sees that the Count casts no reflection in his shaving mirror. The Count understands the danger posed by the mirror's revelation. He grabs the mirror and smashes it, calling it a "foul bauble of man's vanity." But do we look in the mirror only out of vanity? No, for Lucy has looked in the mirror to learn how to read herself, as she writes to Mina, "Do you ever try to read your own face? I do, and I can tell you it is not a bad study." Poor Mina will have her own mirror crisis; looking into a mirror, she sees the foul "red mark" on her forehead and "knew that [she] was still unclean." The Count, however, can never know himself in this way; he cannot read his own face because he can never see it reflected back to himself: he can't see himself as others see him.
Just as Stoker denies the Count a mirror image, he denies him a place in the documents that mirror for us the events of the novel. We have the words of the Count recorded by others, but the Count is never reflected in the mirror of a diary. This absence makes the Count strange to us, and also strange to himself. That makes me wonder what would have happened if Seward had tried to record the Count on the phonograph. I imagine that just as the Count's face cannot be seen in a mirror, his voice could not be recorded by a machine. Just a guess, though: what a fascinating experiment that would have been for Seward and Van Helsing to conduct in the name of vampire science!