I hesitate to step into this maelstrom, but by applying Kate's answer I believe the specific answers to Acorn's questions are:

1. v15.0.0.0 + bug fixes
2. v14.4.0.0 + bug fixes
3. v12.0.0.0 + 27 bug fixes
4. v12.4.0.0 + 23 bug fixes

That's my best understanding of the system. But I may be wrong.

Phil