As D&D Next and eventually 5e were coming out there was a discussion about whether or not questions from the playtest should be tagged separately from questions about the edition upon its release (How should we tag the "next" edition of D&D?). The winning answer and policy we went with was Magician's answer to just transition dnd-next to dnd-5e as a synonym and let questions be updated to reflect the published released rules of D&D 5e.
For general questions I agree with this, however I have a few, and have seen a few other questions that are specifically asking about playtest rules or adventures written for D&D Next playtest versions (such as Dead in Thay, Ghosts of Dragonspear castle), where this seems less applicable.
My own question asking about creating characters above level 1 for a Dead in Thay game (Does D&D Next or Dead in Thay have rules for equipping new PCs above level 1?) just elicited an answer referencing the DMG despite it stating in the title and body of the question that this was a question about D&D Next rules.
Should D&D Next have its own tag to prevent answers like this from popping on on playtest specific questions?