This is common to happen any time a sequel or series-continuation is recently released. All you need to do as a question author is make sure you state the name of the game you are playing, and tag it appropriately. If you don't have the reputation to create a new tag, see this FAQ.
While it sometimes will help to add a notice explaining which game you are referring to, this is ultimately redundant noise as the game you're talking about should already be clearly established by your question body and tags.
It's also an ephemeral problem - once the immediate popularity dies down, the "notice" becomes worthless and tiresome noise to deal with. So having those warnings means that a few months down the line, we're going to need to go back through all of them and remove it. Unless we want to go back and start adding these to questions about Assassin's Creed, Ogre Battle, and every other non-most-recent iteration.
If someone answers your question with non-applicable content from the wrong game, it is no less off-topic if the game is part of the same series than if it was a completely different game. Comment them explaining that your question is explicitly tagged for the earlier game, and throw in a downvote if you don't feel merciful. It's unwanted noise, so don't feel bad about downvoting in this situation because that is exactly the kind of thing downvotes are used for.
Answerers should be giving the benefit of the doubt to the way that the question author phrases the question, instead of assuming that the author must be mistaken. To be honest, it's very rude to disregard what the author has clearly written and tagged.
If you think the author is very likely to be referring to the wrong game, then the better option should be to add a comment asking to verify the game. If the verification clears, then you can post your answer (maybe store it in Notepad while waiting?). If the verification doesn't clear, then at least now you don't have to sit with a downvoted answer for being off-topic.