They wouldn't allocate the other two frequencies close enough for interference to ccur.
Actually that's the whole point of the 8.33 kHz transition. There is (allegedly) a shortage of frequencies at the moment. By reducing the spacing from 25 kHz to 8.33 kHz we triple the amount of frequencies available.
So pretty soon after the 8.33 kHz transition is complete, you'll see frequencies being allocated that are only 8.33 kHz apart, and whose DOC is close enough to cause interference if you still use them as if they're 25 kHz frequencies.