While LIC.DAT deals with disc-based game authentication, the act.dat file is related to user account activation for PSN content (PKG games).
Mastering the PS3: A Deep Dive into Generating LIC.DAT Files
If you’ve ever tried to launch a PS3 backup only to be greeted by a "Renew License" error or a black screen, the culprit is often a missing or corrupt LIC.DAT file. This small file lives in the LICDIR folder and tells your console that the game is authenticated.