Logic Elements size differs without changing source

Is Quartus reusing the results from a previous compile? I found out that even if incremental compiling isn't enabled, compiling from a project folder that already has a compiled project will produce a different result than a clean project folder (removing the db and incremental_db folders is enough to "clean" a project).

If you are regenerating a SOPC Builder or QSYs project before you compile the Quartus project and are using a system id component, it will also produce a different result each time because the timestamp date and system ID code will be different. It shouldn't generate a change in logic usage though.