You might have already concluded this, but if one were to guess, based on the discontinuation of the Greyhawk product line in 1993 and the other products that he was associated with, it's likely that he started it in 1992.  Since he was heavily involved in other Greyhawk publications, such as From the Ashes, which was completed in 1992, it would be most plausible that he began working on Ivid the Undying during, or after, finalizing the boxed set.  Since TSR discontinued the product line in 1993, there probably would have only been a window from late 1991 to early 1993 where he could have worked on it.

Hopefully another Acaeum member was involved or has additional details.

grodog wrote in Ivid the Undying solicitations?:Since Ivid had both a stock number (9399) and a cover mock-up (discussion in the Library and Research pages here), was it ever solicited by TSR before it was killed as a project, and later excerpted in Dragons 204 (April 1994) and following?

I ask since I’m trying to get an idea about when Sargent first drafted Ivid, to trace some of the inspiration for his additions and tweaks to the setting beyond Cook’s Greyhawk : Wars boxed set.

Allan.

I'll also take a look through the stuff I have picked up to see if it was mentioned/planned in those years.

If you uncover anything relevant, please let us know.