Re: Main PoE code and Backer Beta, the way this usually works is this:
1. There is a main code branch (AKA trunk) where everyone does the actual programming (or the actual programming happens in separate branches which are then merged into the main branch upon completion). All the bug-fixing happens here.
2. There is a separate code branch ("release candidate", though the name may be a misnomer) used for testing and bug-hunting. This branch is made at regular intervals.
3. There is likely another separate code branch ("backer beta") which was created from one of the "release candidates" (possibly the most stable one in recent history) and then customized by cutting content down to its present size.
The way a new BB version can happen is twofold:
1. They can create a patch from the main code branch and apply it to the BB branch. This carries a risk that the main code branch is too divergent from the BB branch and the patch will be a nightmare to apply and merge.
2. They can create a new RC which includes bugfixes from the main branch, then ensure it's stable, and then create a new BB from it. This may be more or less difficult than option (1), depending on the method they applied to cutting content. If content is loosely coupled from code and can be parametrized, then it's not a big deal. If it's not, then the work required to make a new BB is probably too much effort.