they dont count all of clicks.
in their pannel , in menu->all links , links stat show click but at the end of the day the click didn't count .
how possible ?
Most url shorteners count unique visit per 24 hours.
If you have some users visit more than 1 time, it counts only 1.
Some other factors will also affect the counts such as VPN, adblock, change IP, invalid countries, etc.