Williamina Fleming says of this, "A large patch of faint nebulosity, probably connected with [the Great Nebula in Orion]. NGC 1999 is near here, but the description given is unlike that of this object." NGC 1999 = H IV 33 is a "* 10, 11 in neb" at its place about 5-6 arcmin south-southeast of the center of IC 427. It must have appeared as a simple star on the Harvard plate.
IC 427 itself is about 10 arcminutes across, but is immersed in a much larger nebula roughly 25' x 20' that also includes NGC 1999, and is connected to IC 428.
See IC 434 for a bit more on this area and the IC nebulae here.