Which of your examples is true? None of them, because they are all practices, and no practices are true in themselves. They are gimmicks, means to an end. You've pointed to Buddhism's capacity for offering different approaches to practice to different communities of practitioners, and to different individuals, at different times (most of which have existed simultaneously in spite of claims to having superceded one or any of the previous). How does this reflect a contradiction? It reflects the contradictions of the samsaric world we inhabit. The monastic path is available because it is of benefit to some; the tantric path is available for others for the same reason. Not mentioned in the sutras, but also available: getting whacked in the ass by an old man with a stick at a Zendo. All means to an end: different iterations reflect differences in means, not ends. 84,000 Dharma gates to deal with 84,000 kinds of screwed-up people. One Dharma.
Nichiren claiming that his path is the only means to liberation in our age isn't a practice, it is a doctrinal position. Buddha claiming that celibacy is needed for the eradication of passion which binds us to this world is also a doctrinal position. Also, the tantric path is practiced by monastics in Tibetan Buddhism and in all forms of Buddhism prior to this celibacy was required for monastics and breaking it was reason to be dismissed from the sangha. Who has the correct view?
This is why I say that your hypothetical is meaningless because you haven't given a specific instance or even a hypothetical context in which a teaching that is said to be Buddhism but which is also not Buddhism could be plausibly Buddhist to anyone. When has this happened, or when could it? Until you specify this, your analogy cannot be taken seriously.
My hypothetical scenario was directed at the idea that Stephen Batchelor's Buddhism is in fact Buddhism or part of continued revelation. Buddhism is a spiritual doctrine of awakening that aims to guide us to nirvana in order to avoid continued transmigration and suffering in samsara. Batchelor denies this core tenet, and yet, as has been pointed out, many follow him and consider themselves Buddhist. Why then can't the other core tenets also be contradicted (as in my hypothetical scenario) under this line of thought? At least in my hypothetical scenario the degraded practices I described can, according to my hypothetical doctrine, lead to liberation from the wheel of birth and death. Batchelor denies this outright. How is this Buddhism? Hint: it isn't.
Basically, it is really pretty simple. All yogic paths in Indian religion and its offshoots, whether Buddhist, Jain or Hindu, whether in India or Tibet, or China, etc., accept one thing in common: in order to cease taking rebirth in samsara, one must deal somehow with the kleṣas that drive rebirth.
That is true, but their views on the means to this can be deeply variant. I wonder if Gautama would accept the Aghori practices of consumption of human flesh, piss, shit, and liquor or the Thugee's practice of ritual murder in honor of Kali as acceptable. I'd wager he'd maintain this would send them to hell. Thus it seems to me that there must be some standard set as to what constitutes Buddhism and likely the best way to uncover that would be to look at its earlier history. It seems while Hua-Yen metaphysics or Zen koans aren't explicitly present in earliest Buddhism, they still manage to incorporate the earlier standards without contradicting them, whereas tantric practices and Nichiren's claims, for example, are questionable in relation to the earlier standards and doctrines.
So, if you approach from the teachings of Nichiren, you find the Buddhadharma in the Daimoku. If you go from the teachings of Shinran, you find it through the Nenbutsu. There are many entrances, many teachings. But they are not unrelated, they don't come from nowhere, and every Buddhist teacher establishes the teachings on the words and realisation of Shakyamuni Buddha.
I have no issue with the idea that there are different means that may lead to liberation that aren't found in earliest scriptures. What I am saying is Nichiren claims that Daimoku is the only means for our era. That contradicts your very message about many entrances, at least for our Latter Day of the Law. Same thing with the issue of celibacy and tantric sexual practices. The latter isn't taught by the Buddha and contradicts his emphasis on celibacy.