You can export the board data using File - Export - Design Data and then import it into the other boards, or if you just want the Board Outline etc you can export IDF from the same File - Export menu, both of these are in Expedition PCB.
As you probably have noted, a simple copy paste into a new directory didn't achieve satisfactory results. This is because for each design, the ID's are different for each board as packaged. Try the following sggestions:
1 - Ask your salesman about a tool, called Variant Manager that was designed to do this.
2 - make a template of the primary PCB and use it for the alternate Boards. Nets and Components should sync to the new ID's
3 - change the desired methodology and make multiple projects, each with one board using the original design as a master template.
4 - create a format reuse including the PCB, place the reuse in the design and smash it.