One of the rules for nouns is that the negative examples you use (in the whole sequence, including testing) are ones the learner already knows. In this case, I think that, because there is such a narrow range of variation in letters, they felt like the already-known “d”, “p”, and “q” could be saved for the test examples.
I personally think it wouldn’t hurt to mention them before the testing examples, too, and this seems like something open to interpretation.
One of the rules for nouns is that the negative examples you use (in the whole sequence, including testing) are ones the learner already knows. In this case, I think that, because there is such a narrow range of variation in letters, they felt like the already-known “d”, “p”, and “q” could be saved for the test examples.
I personally think it wouldn’t hurt to mention them before the testing examples, too, and this seems like something open to interpretation.