Secret Squirrel from the Faeit 212 inbox
The imperial guard sketches are from "the gothic and the eldritch: the collected sketches of Jes Goodwin" which was published in 2001. The guard sketches themselves are from 1993 and there are more than just the 4 (although they're not in the book), some of which were used for the 2nd edition metal guard models.
All that said, you can't discount any old sketches as Jes also make concepts for high elf reavers back in 1992 which are almost exactly what is in the isle of blood box set.
Here are some of those pics