On my trip in May, I was speaking to the guides and was told
ABD might be telling you who the Guides were going to be prior to your trip, now how far in advance you would get the notice they didn't know. This was being done or at least contemplated because there were people who complained that the guides in the brochure, the pre trip booklet you get in the package that is sent 45 days in advance, were not the guides on the trip, in fact there was one person who was so upset she was yelling at the guides that her trip was ruined because they had male guides and not the female guides in the picture.
Now whether this will actually occur remains to be seen but one of the guides on my trip was the guide that was yelled at for not being the guide in the book.