Please read the following information from our website:
Current rating is based on the last rating the player has entered a match with. Therefore, promotions and demotions will usually be delayed by one match. We also only collect recent matches. If you’re new to the site we may have missed old matches.
The above doesn’t apply to Immortal rating and above, where the rating is updated from Riot’s official leaderboards, usually once an hour. Rating changes happening between updates are generally lost forever.
Remember that “anonymizing” your leaderboard placement in-game will also stop us from tracking the exact rank. Your rating will show up as just “Immortal” or “Radiant”.