The way Wot Numbers pulls data from World of Tanks is by listening and reading data from two files that WoT client updates (dossier file) and creates (battle file) after each battle.
It is very important to start Wot Numbers and keep it running while you play WoT. This makes it possible for Wot Numbers to record results for each battle.
The dossier file includes total statistics for all tanks, this file gets updated after each battle. This file has limited battle information.
The battle includes more detailed battle information. WoT creates one battle file per battle. These files are only created if the player opens the post game stats after the battle has ended. Ignoring this step will cause some battle data to be missing from the battle view (like credits, map and actual XP including mission bonuses).
This problem will be reduced if you install the Battle Result Retriver (BRR) mod from menu: Settings + WoT Game Settings. This mod will force WoT to create battle files for finished battles without having to open the post game stats. This mod is not 100% reliable, even when using this mod you might have to open stats manually from time to time.
Here's an example from the battle view where some battles have incomplete battle details due to missing battle file:
Battles marked by a row number in red instead of blue indicates that the battle-specific file hasn't been produced, and thus some values are missing.
Typically this happens if you are killed and you exit to the garage before the battle has ended. However, this doesn't mean that you have to stay and watch the entire battle. You can open the post game stats from the notification center at a later time, and Wot Numbers will fill in the missing data. Just remember to do so before closing the WoT client, since the notification center gets flushed when you exit.
You may also have noticed the Result and Survived columns saying "Several" or "Some". This means that Wot Numbers has recorded several battles into one row, normally because Wot Numbers wasn't running while you were playing or the post game stats was not displayed for the individual battles.
If you're starting Wot Numbers after having fought several battles in the same tank, Wot Numbers isn't able to distinguish what happened in which battle. Instead it displays one line for each tank that has been used during this "blackout" period. Note that on these occations you can hover over the Tank Name, Result and Survived columns to to review the number of battles, number of vitories, etc.