I came across a question about a demo that has been released. The question is entirely answerable, but this lead me to look up how many demo related tags we have. I found three matched the search results for "demo":
I see good reason for the use of the demo tag. However, I consider it a grey area, concerning whether the questions would apply to the full release, as well.
Questions that are specific to the demo
These questions specifically apply to the demo, but in both cases, they ask about availability of a certain feature. It could be argued that complete answers could only be provided through a comparison of what is available in the full game.
In this question, a user asks how many videos are available in the demo.
In this question, a user asks about the feature limitations of the demo.
Questions that might differ in context
These questions may apply, completely, to the full release. Due to developer changes before release, they may not.
In this question, this question, and this question a user asks how to beat the boss at the end of the demo. This could greatly change for being in the demo, as the demo might limit strategies the player could adapt. Furthermore, the boss might change before the final release, either due to last minute changes or the developers simply making the demo version more difficult.
In this question, the user asks about a secret passage in a level of the demo. Again, this may have changed for the full release.
Questions that directly relate to the full release
These questions are still in context of being a demo, but are related to the full release.
In this question, a user asks about transferring save data, from the demo to the full release
In this question, a user specifically asks where to obtain bonuses that can be transferred into the full release.
Instead of having a tag for each game demo, would it be better to have demo as its own tag? Questions relating to a games demo could be tagged as both demo and the game title. Questions relating to the full release would more likely be received by users patrolling that games questions, and at the same time, it would be easy to infer if the user is playing the demo or the full version, by their inclusion of the demo tag.
The demo tag could have a disclaimer in its summary to include the tag related to the game title the poster is playing. Users would be able to easily identify the secondary requirement of a "title tag", and it would be easier to tag questions in the future, where the poster makes it known that they are playing the demo of the game, but tags the full release title due to lack of a tag for the demo.