> exec and trackdisk where almost not changed since 1.3.
> everything for what 1.3 is used is still in 3.1

You are mistaken if you think that a license granted/obtained for a specific version of a software automatically extends to prior versions of that software, just because the licensed code is built upon the older code. That's not how copyright works, at least not in EU and US. And if it's "almost not changed", as you say, then why not simply use exec library and trackdisk device of licensed 3.1?