I have found a list of tags in a sticky post in the Beersmith 2 Questions posts (http://www.beersmith.com/forum/index.php/topic,6200.0.html) it is about halfway down, recipe_tags.txt created by tom_hampton
I have searched this list and everywhere else and like you I'm still looking for Measured Pre-Boil (Post Mash) Gravity (Session Tab - Volume and Gravity in Boiler) if anyone knows if the tag exists.