Again, as readers, I think we should know better than to expect Google-like answers from Tarot. I think the cards are never wrong (in a sense, they can't be "wrong" or "right" as they are just pictures on paper), only that we ask the wrong questions or interpret them wrongly.
Here's a little anecdote about accuracy, but be aware I'm not asking for sympathy in telling this, just telling it as I've been thinking about a certain reading, recently. I'm going through a weird time right now, being evicted from my apartment, staying with friends and looking for a job, but my biggest concern was my cat; I had nowhere to put him. A member on AT here did a reading for me about him, and I won't go on about the whole reading, but the final outcome, was the Fool, and that person interpreted him as a saying that in the end everything would work out for us, and that I wouldn't have to give him away and the surrounding cards certainly made sense in that prediction. Well, as it turned out, I left him with a friend who couldn't keep him as he already had a cat and they didn't get along, so I put him in a friends closed yard, where he stayed for a day while I was there, and then ran away when I went food shopping.
Now, in retrospect, I think the Fool fits the scenario perfectly, at least for him. What is more Fool than running away, especially for a cat? I think that reading was spot on, even though I didn't see how it would turn out at the time. And perhaps I did understand what I wished, since of all the ends I could foresee, I must admit I didn't see that coming, which, in a sense, only reinforces the Fool.
So, ultimately, I don't think readings can be measured for accuracy in a dry sense, especially not predictive readings, since we may not understand the reading at the time, and that misunderstanding is part of the future, so to speak. Readings can be measured for accuracy when dealing with the past, but again, it's never black and white. Like I said in an earlier post, Tarot at times shows us what was, but it also may show us what could have been; what is, or what should be. I trust it as far as I can, but in a sense it's like walking on light, not a solid earthen floor.