A handy tip from the starter design library from Optimum Design Associates ("Mentor_PADS95_PADS_Net_List_Library_Guidelines_Rev1a.pdf"):
"Symbol
REQUIRED: The value of this field determines the symbol that will be used when the device is selected from DxDatabook for placement on the schematic. The exclusion of a file extension (.1, .2, etc.) in the symbol name allows the use of any of the multiple symbols with the same name. For example, cap.1, cap.2, cap.3, or cap.4 can all be selected from DxDatabook for any device that has ‘cap’ as the symbol name. This allows for different rotations and views of the symbol to be selected for placement. And asterix character at the end of the symbol name allows for all symbols in a Hetero set to become available for placement on the schematic i.e. xc7vx415t-ff1927* "
Mentor's "DxDataBook Setup (Beginners)" is a good reference too: https://supportnet.mentor.com/portal?do=reference.tutorial&id=MG576734
I'm still trying to figure out where DxDatabook finds its symbols...