The AmigaOS 3.9 code was largely unavailable for development work. What remained and was availabie is material which was licensed for inclusion in AmigaOS4.

What we got here is a mix of the AmigaOS 3.1 code (bug fixes galore, plus enhancements), the 3.5 update, the 3.9 update plus completely new software such as Disk Doctor V2.134 (written from scratch to support large storage devices and all Amiga file system flavours descended from the 1986 default file system; this is not your father's Disk Doctor any more).

The other reason why it's 3.1.4 is that we realized early on that we could not continue development of the 3.x line anyway, so we joked it would have to be an irrational version number instead, perhaps one digit at a time.

Good old "PiVer", the TeX approach to versioning: https://en.wikipedia.org/wiki/Software_versioning#TeX

Thanks for clarification. And thanks for Term and MagicMenu (and all the other work) ! :)