The Confuser was not written by God but by mere mortals, and there are a lot of errors in the questions/answers. This is probably one of them.
Here's the current schedule and validity period of all the metforms:
Met Office: Aviation - new briefing charts
Looking at that table it looks like there's a difference between the forms even. Spot winds (214) have a six-hour cycle and a six-hour validity (but are issued three hours in advance) while sigwx (215) have a six-hour cycle with a nine-hour validity (and are issued five hours in advance). The European equivalents (414/415) are on the same cycle.