Usually, the textual description matches the numerical requirement at the bottom, e.g.
"You need to reach level 150" and below it, xxx/150
"You need to complete 1000 quests" and below that, xxx/1000
"You need to explore 1000 rooms" and below that, xxx/1000
"You need to get 1000 bonuses for visiting friends", below it xxx/1000
"You need to add 300 friends" and below it is xxx/300
"5000 points of energy, you are about to overshadow the sun" xxxx/5000
"2500 explorations without any result" and below that, xxxx/2500
However, for opening chests, the description says "Open 500 chests" and below that is xxx/625.
Thus there is an error somewhere. The description on MM should have said "Open 500 more chests" or "Open 625 chests".
For the sake of consistency, 625 chests should be listed on our chart, and not 500.