Hello,
I have B4A projects dating back to B4A 1.5. As matter of fact I am currently updating a project, using B4A 3.5, that was written with B4A 1.8. I had absolutely no problems opening the older project and working with it with the newer version of B4A.
When I upgrade to a newer version of B4A, I have always installed it into a new directory, for example "C:\Program Files (x86)\Anywhere Software\Basic4android35" for the most recent version. I leave the older version on disk in its "last used state" just in case I ever have to return to it. So far I have never had to return to an older version.
I think, however, there will be a problem if you take a project edited on a newer version and try open it with an older version. Some features of the newer versions are not supported by older versions.
B4A has grown with some amazing new features since your older version.
Barry.