One way not to go is to define the problem away. Scott, for example, doesn't even think the dogmas of the Immaculate Conception and the Assumption are instances of DD at all; instead, he says, "they're pretty straightforward teachings of the Church." Now I agree that they are at least relatively straightforward teachings. But it follows that they are not instances of DD only if one also assumes at least one of two things: (a) that no result of DD is such a teaching, or (b) that both teachings in question follow neither by deductive necessity from the normative sources (and other, equally unexceptionable premises) nor by some form of induction therefrom. I can find no justification for either assumption. Obviously, (b) is unacceptable because tantamount to claiming that neither dogma is latent in the deposit, which contradicts what has already been admitted. Nor does there seem much reason to believe (a), i.e., that only non-straightforward teachings—arcane or roundabout teachings, perhaps—count as instances of DD. The way to determine whether a given doctrine has developed is answered not by assessing complex or simple it is, but by learning whether or not the form of it we now profess was known and professed by the early Church. If it was not, then it's an instance of DD; if it was, then it isn't. By treating as irrelevant how late the two dogmas in question are, precisely as dogmas, Scott effectively tries to define the problem away with an implicit definition that may be stipulative but certainly isn't persuasive.
I've urged that some DD is "ampliative," meaning that its legitimate results amplify our understanding of the depositum fidei without being formally deducible from the normative sources and other, equally unexceptionable premises. So much seems obvious to me in the case of the Immaculate Conception and the Assumption. What's implicit in them, in a non-technical sense of 'implicit' synonymous with 'latent', is made more explicit by a kind of abduction: inference to the best interpretation, in this case of the sources' larger meaning and purport. That's what the papal documents defining those dogmas do, by way of boiling down what the sensus fidelium and the labors of theologians had been doing for centuries. I've also suggested that the DD process may work similarly to how the sensus plenior in Scripture does. Thus, just as the meaning of older texts gets amplified and filled out by later ones, as happened to the OT in the NT, so too does the meaning of various professions and formulae of the Church get amplified and filled out by later events, reflections, and efforts at interpretation. That would hold not just of the two defined Marian dogmas, but the more offensive ones of papal infallibility and the filioque too.
Now Scott is, rightly, a big fan of Newman's. But it seems to me that Newman's seven "notes" of "genuine" development, if substantially reliable, indicate that genuine DD need not be deductive and often is not. Such notes would not, for the most part, even be relevant if all genuine DD were deductively necessitated by statements the normative sources and other, equally unexceptionable premises. The seven notes work as a way of assessing the plausibility of essentially abductive interpretations. So I'm mighty puzzled by the fact that a Newman fan has been defending a strictly deductive model of DD.
I say "has been" because Scott is feeling for some common ground between us. While continuing to insist on a sharp distinction between inference and interpretation, and now also between both and inspiration, he is willing to grant that some of the premises needed for deductive DD can be arrived at by some-or-other form of induction. For the time being, I am content with that. If a given doctrine is what I call a "legitimate" and what Newman calls a "genuine" development, then it is certainly true as belonging to the deposit of faith; and if so, then there is at least one sound deductive argument for it. But as I asserted a few posts back, the deduction is often just "icing on the cake." The real work of DD takes place by means of interpreting the sources in such a way that premises for a sound deductive argument, if that's what's sought, can be provided. And I would still insist that such work typically takes place by a kind of abduction that I've called "inference to the best interpretation," which is akin to how Aristotle says we know by induction that all humans are, necessarily, mammals. The value of Newman's notes lies in their efficacy as a test of such explanations.
Examples are surely needed. I offer two: the dogmas of the Immaculate Conception and papal infallibility.
The DIC cannot be proved from Scripture, the creeds, the liturgies of the first-millennium Church, or even popular devotion, if by 'proof' one means a deductively sound argument whose premises require no inductive support. The development of the idea of the Immaculate Conception occurred as a way of accounting for a number of things: as Theotokos, she had to be a "fitting vessel" for God the Son; she was acclaimed as the Panagia or "All-Holy" fairly early in the Eastern churches; as paradigm of the disciple, she had to be the most perfect instance of a child of God by adoption. Neither severally nor collectively do such data allow one to infer deductively that Mary was always free of the stain of original sin and that such an affirmation was always latent in the depositum. Indeed there were technical objections, such as Aquinas', to overcome. But once those objections were overcome, the DIC emerged in the Catholic Church as not only plausible but also as an almost irresistible interpretation of the relevant data. The process of arriving at it was a case of inference to the best interpretation of the data I've cited, and others. Deductive argument for DIC, if desired, adds nothing to the content or persuasiveness of that result. The real work is done by a kind of induction, in this case by a kind of abduction. And that work survives the test of Newman's seven notes.
The example of Vatican I's definition of papal infallibility is similar and even more pointed. Rome had always maintained, when the issue came up, that the teaching or ratification of the Bishop of Rome was necessary for a given doctrine to bind the whole Church as an object of the assent of faith. That appears to have been the common view throughout the Church up through most of the first millennium. But of course it does not follow, deductively, that the definition of a given doctrine by the Bishop of Rome would itself be sufficient to so bind the whole Church to that doctrine. That only follows if one assumes (a) that the Church as such cannot teach what is false as a doctrine belonging to the deposit, and (b) by virtue of his apostolic authority, the Pope speaks for the Church as such. There is general agreement between Catholicism and Orthodoxy on (a) but not on (b), which is a development not itself secured by deduction from unexceptionable premises. But (b) is one possible explanation of a doctrine that was held in common through most of the first millennium. Its plausibility as an interpretation of the normative sources emerges from a confluence of factors: the sources themselves, the common tradition for dealing with the decrees of councils, Rome's record of orthodoxy, and consideration of alternative ways of explaining how the teaching authority of the Church, evident in the sources from the beginning, binds the Church. Like any induction, the interpretation that got defined at Vatican I is not logically necessitated by such factors. But it is plausible enough, in Newman's view, to pass the test of his seven notes.