There are 21 safehouses in total in GTA Chinatown Wars: 14 are purchasable, 6 are unlocked after completeing certain missions and one is won with a scratch card. What I suggest you do is to search the entire city for any unpurchased safehouses. If there are any, buy them. Then win the scratch card safehouse. Once you have done so, complete every mission and random encounter in the game, and hopefully, you should own all 21 safehouses. However, if you still have 20 safehouses in your stats, you have a glitch in your game.