I wondered that about the gap too, Laura. 12 weeks is somehow easier to keep track of than 16. I could donate now, but have to wait until April here. Don't like the appointment system either. It never seems to lead to any less of a queue.
For the poster who asked about transferring between English/Scottish/Welsh systems, it sort of works. You can donate immediately anyway. They've probably got better records over the years, but I've had 2/3 bronze badges awarded before finally getting to silver. As long as you're not too worried about that kind of thing, there shouldn't be a problem.