I did a test . I have created a small solid with CE12. Then i imported it inside "Delcam Excange v2015". It works but is necessary clicking on a flag "try conversion" and it's possible that not all surface come imported.
v2015 support ACIS 2300 like CE11.
v2106 support ACIS 2400 like CE12.
Probably with this system you can export your project created with CE12 in another format readable with CE11 or other software.
I hope I was helpful for your problem!
If your file created with E12 is NOT an NC file but a part or assembly file .elt you can try with Delcam Excange 2016. It should open Elite v12 native file then you can convert them in another format like stp,igs..