There is no publishing date in my Snapshot of Krakow, Warsaw and Gdansk. In August , 2015, it is NOT more convenient to take the bus from main station Krakow to the salt mine; the bus route changed due to construction. See their website www.wieliczka-saltmine.com/. I took the train for only 6 zloty roundtrip from the Main Railway Station in Krakow (Dworzec Główny) to the Wieliczka Rynek Kopalnia train station. You can buy a ticket onboard. It was a 3-minute walk to the mine.
If you haven't already, you should also send this (as well as your Schindler Museum update) directly to Guidebook Feedback, using this form: http://www.ricksteves.com/forms/guidebook-feedback-form