Ancestry almost never indicates what the update is, unless it is a big one.
In the case of the Beta City Directories, however, this represents a major improvement over the old city directories database. There are many more city directories (especially in the 1930's - 40's time period). Also I have had MUCH better success at locating someone in a city directory. I'm not a techie, but I know that the process of making the city directories searchable has been much improved.
I suggest that you try your searches again. You can just use the search facility and enter your ancestor's name and city/state. You should find more entries than you did previously.
The Beta city directories database is especially good for finding 1940 addresses so you can search 1940 census, but there are lots more earlier years that have been added too. Worth the time to try it out in my opinion. I've had great success with it.