Thanks for the kind words about Veritas Prep!
The top business schools typically release their essays between May and August every year. I know that's a wide range... Assume that by late July all of the schools you mentioned will release the coning year's essays. If you haven't done so already, you can go to our blog (http://blog.veritasprep.com
) and search on "[school name] essays" and see when last year's essays came out... The latest one among the schools you mentioned was in late July, I think.
You're right that the essays don't change much from year to year. Usually schools do some "nip and tuck" work from year to year, replacing one essay here and refining a question there. Radical changes are rare. So, starting with last year's essays (to start brainstorming on topics) is perfectly reasonable.