Read this topic: No High/Lows, where is history and graphs data used for, and ? cron ?
The cron-job takes current weather-values and saves them to the history if they are higher / lower then the previous values.
So your history covers only a few days.
To get the high-lows from the past years you should run one time a script to read all your past weather-data from WU and filter the highest and lowest values to populate the history file.
Then the cron-job will maintain the history by checking every 5 minutes if the current values are higher or lower then the ones in the history.
Wim