Also on old instances these frames don't exist. I'd rather say :
If encounter has bossunitframes and list of bossunitframes contains unitid from libbossids, then rename encounter to unitname(libbossid).
I have no problem to commit a couple of numbers each contentpatch. Don't worry about that.
The BossUnitFrames exist for "important" adds and the boss itself, so i think it is possible to relabel the fightname in recount and detect it as bossfight without argueing wether the adds can be considered a boss or not.
Would we be able to somehow put the correct bossname to fights like madness of deathwing , like checking which bossunits are up and if it matches one of the ids in libbossid, use that unitname as name for the encounter?