Given the variety of types of DnD over the years, I think it's fair to have several tags for DnD.
For example, there are a lot of DnD3.5 players who might outright want nothing to do with DnD4.
Likewise, chances are a DnD3.5 player will be thoroughly confused by an ADnD question.
We should reduce nonetheless;
I think [dd-encounters] should instead be [dd] and [encounters]. [dd-encounters] refers to a specific Wizards product/program, and is appropriate.
Unquestionably [add1] and [add1.0] should be merged.
I also think [dd] is too vague, given my above point; one should have to be more specific.