there is no problem opening earlier versions of fla files with later flash pro versions (except for as2 containing files and flash pro after cs6).
so, you're ok.
except, and this is an excerpt from a book i wrote (Flash Game Development: In a Social, Mobile and 3D World),
Spreading code across more than one frame of a timeline and especially in more than one timeline is a time-wasting mess and strongly discouraged. Anyone who has ever worked on a Flash file with significant bits of code spread over more than one timeline more than a few weeks after creating that code understands the incredible amount of time that can be wasted looking for pertinent code.
The worst offenders that I have seen (and I have seen hundreds of problematic Flash projects), in the highly competitive worst Flash coding derby, are templates sold by websites like http://www.entheosweb.com/. Do not be fooled into thinking you can get a head-start on a project by starting with a web template offered for sale. There may be some well-coded templates sold online but I have never seen one.
