I'm not sure what you mean by trendlines. Are those simply the lines themselves or the lines you get when you enable for example the linear option under Trendlines (on the Expressions tab). See attached example
If there are many values for a particular combination of dimension then it will result you in "Null". If use sum around that field name then it will add up and show you the consolidated value for that combination.
You need to use Aggregate functions like Sum, Count etc in Expressions to the get value by the dimensions. For single date and point you have multiple scores, if you want to get by Date and Point then you have to use Sum(Score) and use the dimensions date and point. Sum() is similar to Group by in SQL