5 years at Google is forever, and it's not uncommon at all for people to jump around projects at the company. It's also a full year beyond what's necessary to vest. Really silly way to write that.
Typically there’s also a ‘Cliff’ at the start - a period during which no options are available to you.
addendum: the ‘standard’ Silicon Valley stock option deal is: 4 year vest, 1 year cliff.
Eg: first 12 months, no options
Day 1 of 13th month - 25% of your options are available to you
Then the rest of the 3 years vest at a regular pace with the remaining 75% of your options dropping on a monthly cadence
The exception being Amazon who basically give you nothing for 2 years and then ramp up significantly.
This helps them reduce compensation during hard times. Salaries are very sticky; it’s hard to cut salaries. So they offer RSU comp because it’s tied to stock price. When the company is doing poorly, they can pay less. But it also lets the pay high compensation and retain long term talent.
In addition to the initial grant at year 2 during your review some employees get more shares on top of the initial grant(that vest over a certain time frame, usually 2-4 years), these are called stacking RSU grants and its why people stay at FANG companies a long time as these grants stack higher and higher all the while your career progresses and the company stock goes higher.