Maybe because I think of a 1 year booking window for airfare plus 1 year to plan and accrue miles for trips? (milenomics.com)
For this reason, it's worth looking into the programs you plan to accrue miles with to make sure you're ending up with a (relatively) favorable award program. (theglobetrottingteacher.com)
If you have employee cards, their purchases will also accrue miles at the same rate. (rewardexpert.com)