Oxford's "self-sponsored" results include those doing the integrated course and those doing the 26 week full-time modular groundschool, but not the distance learning modular students.
There is nothing sinister in this - we are not trying to 'massage' the figures. But distance learning students make their own arrangements to take the exam, sometimes at Glasgow, sometimes at Silsoe, etc. We only find out their results if they bother to let us know. Some do, some don't. We suspect that those who do are more likely to be the ones who have passed and that this will bias the results in too favourable a direction. So, in the interests of ethical business practice, we leave them out when publishing our figures.
However, we're quite happy to explain how we compile the figures, so there are no dark secrets here.