Amazon chooses which Child ASIN is advertised for a keyword based on the performance of that ASIN. So what does that mean for Scope? 

You may notice a drop-off in the Keyword Position History graph for one child ASIN, but if you navigate to a different child ASIN and look up the same keyword, the graph picks up where the previous one left off. Let’s look at an example:

I am currently tracking a keyword that has been ranking for Example ASIN1 for some time. I recently noticed that it appeared the Keyword Position History graph for this keyword was not updating. 

As well, when I searched this keyword in Amazon Example ASIN1 did not come up, but rather another child ASIN appeared. I used the ASIN Lookup feature in the Scope WebApp to search Example ASIN2. Once here, I found the keyword and confirmed the position history for Example ASIN2 began when the Example ASIN1's history ended.