I haven't got the details here at work but I log when people register ( and from what I remember most registered before there was any talk of Killian having a go. By the time we get to April then most people have registered.

There was a spike in the mid 1980s and it took until the bump around 2010 for the most successful year to be eclipsed. It's quite possible that the 2010 bump was down to Feet In The Clouds but equally it could be a cascade within clubs - someone does the round and others in their club think "well if they can do it, so can I".