It's not that simple.
The LEL route, entered as a list of controls, is under distance for a 1400km ride (if you were to enter it as a DIY ride) as there is little or no leeway with DIY rides.
Under AUK rules, calendar events are allowed to be slightly under-distance (shortest route) on the understanding that the roads that comprise the shortest route are horrible and no-one in their right mind would ride them. The route sheet will provide a nicer route on more cycle friendly roads. This applies to quite a few calendar events.
LRM has slightly different rules. PBP was under-distance if you chose the right route (but you had to stick to the prescribed route on that ride).
It's all about making something that's roughly the right length that will also be interesting to cycle. Look at the leg from Thurlby to Washinborough. The obvious choice, to knock off 3km off the bottom half, is to just blat up the A15. There are similar things on most legs that would make the whole ride a horrible blat along A-roads if you wanted it.
