I still have an articulate (but incomplete) answer about this topic in my Drafts.
It's incomplete because I'm still in the process of understanding how software release process happens now (post 2015): it's hard to figure out and track down what is the current state of Software Development with respect to what can be learned reading a March 2015 HP document called "Release Process for ProVision Software" (specific for HP 8200zl, 6600, 6200yl, 5400R zl2, 5400zl, 3800, 3500yl, 3500, 2920, 2915, 2910, 2620, 2615 and 2530 Switch series).
A possible short answer could be: use any current software branch (currently active branch is one defined as Current Product Engineering...this with respect to any Maintenance branch eventually available)...you should instead figure out which particular branch within the active ones (as example: KB.16.03, 16.02, 16.01 or 15.18) does what you need mostly (the most recent one - KB.16.03 - includes new features with respect to the others).
A maintenance ("m" suffix) branch should be created every 18 months...but this, as far as I see, is not happening.
