If the reading really seems to scream a particular message which is unrelated to their question, my job is to communicate what the cards are saying, so I communicate it... and usually when that's happened, the client has validated that what I had to say was relevant to something else going on for them.
Sometimes, a card or two will feel separate from the rest of the spread.. like they are talking about something else, and then I speak about them as if they are.
but...... that doesn't happen to often for me, because I really believe that any card in the deck could potentially answer any kind of question about any situation, and to me the client's question, together with the spread position, provide a context for interpretting the card, which automatically relates it to what they asked.
I think that the question can drastically alter the meaning of any card, and often while I'm doing a spread, I reflect on whether or not I'm still answering the initial question, and try to keep on task.
One activity I've done in a Tarot class I taught was to make a long list of questions, and then as a group we think of ways that a single card could provide an answer to all of the questions. This is helpful to stretch ideas about what cards mean, particularly for cards which I tend to generally interpret in the same way whenever I see them..
for example, if different clients were to ask, "what is the root of my financial problems?", "Should I move to a new home?", "what kind of spiritual practices should I embark on?", "where is my lost necklace?", and "how do I get my dog to stop chewing the furniture?" and in each case the Lovers card came up, it would mean something a little different in each case.
This has also been a useful excercise when I've gotten myself into a box of thinking a particular card is 'good' or 'bad'.