What you have discovered is correct. The very first thing I did upon entering our cabin ( the Grand in September), was to call the Dine Line and ask to be on the list for the Chef's Table or Winemaker's Dinner. She took our name and cabin number and said IF there was to be a Chef's Table, then we were on the list and they would contact us later with the details. She also said that there would be no Winemaker's Dinner.
Yes, it was worth it and we received the information just a day or two later after my call to the Dine Line. We were seated at a large square table in the Crown Grill (side room) with about 3 other couples. DH is unable to drink alcoholic beverages so his fee was less, however, they offered him many other nice options during the dinner. It was very impressive and the hosts, servers, and chefs took much pride in what they were doing. We received a very nice autographed cookbook and photograph of the attendees.
I believe that only one Chef's Table is offered per cruise... maybe it depends on the length of the cruise. Ours was 12 nights.