There are a few questions I have found that could use one or both of these tags, and with multiple games in the series now, (for some reason) people can confuse the dark-souls tag as a tag for the series, rather than the first installment.
Normally I would go straight ahead with this, but the issue is that if the community is (albeit rarely) already confusing the tags, adding more would just exacerbate the issue.
Some examples of this might be:
- Lore reason behind dissolving of the corpses in Dark Souls - Uses the dark-souls and dark-souls-3 tags
- Does Dark Souls 2 allow random online mode? - uses the dark-souls-2 and dark-souls tags, yet is asking specifically about DkS2.
- In terms of lore, how do Miracles work? - this question is asking about the series, and has used the dark-souls-3, dark-souls-2 and dark-souls tags correctly, but this is a question that might benefit from a generic tag, as it is not specifically asking bout a comparison between the games, but the series as a whole.