This was something interesting I figured out while doing the Recruit-a-Friend thing with my friend.
If you grant someone a level, they keep the same % through that level that they were, when they level up. This means, if you were to reach 99% through level 1, then level to 30 for example, you'd still be 99% through your level.
I'm not sure if it's a repost, I'm terrible at using the search feature. However, I couldn't find anything.