So let's say I earn 4 weeks per year. Don't take any vacation year 1 starting Jan 1. Still not taking vacation year 2. On July 1, I have 6 weeks in total. At this point, assuming a 1.5x accrual cap, I stop accumulating until I take some time off, at which point I start accruing again up to the same 6 week limit. (So no new vacation time is earned until you get below the 6 week cap. There's really no relation to the calendar year.)

I believe some places pay out unused while still employed but I've never seen this.