Not really, not when you have a book deal, a piece of art for a convention slide, and a public event expecting announcements. The
Prey trilogy was announced more than a year in advance -- it had an approved outline as of its announcement, but the first manuscript wasn't started in earnest.
Kenobi was announced ten months before the book release, and before I began the manuscript. (I had an outline from six years before, so it wasn't starting from scratch, but we weren't really underway.) It
looked like we were much further along because of the painting we released with the announcement -- but that had in fact been repurposed from something done for another licensee. [Edit: I still to this day get people asking about "the original cover" -- they're remembering the promo piece, seen here. It's just a happy coincidence it existed -- it made us look like we were nearly done!]
That announcement was, incidentally, the month after
Sword of the Jedi was announced, and two weeks later the buyout happened. I was concerned from that day until the release that my book would go poof; one of the reasons we shelved the
Kenobi outline in 2007 was because George Lucas had reportedly considered a live-action TV show set in the Dark Times. I expect there was enough doubt at the time as to the future that a trilogy looked like a multiyear publishing commitment too far; Paul Kemp, I believe, also had an announced duology that fell into the same category.