Getting a value based on the rows in the previous date's data and are not in the new

Hello Guys!

There is a topic where I would like to get help in, because I think the solution is pretty obvious I just cannot find it. I have a table which gets the data from a folder of .json files which are being generated every day from jira. There sum remaining hours of each issue keys which are important. 

This data is being loaded to the same table, and being divided by the "Date created" column. My question is, that how do I get the sum remaining hours of the issuekeys, that were part of the previous generated .json file data, but are no longer in the new export? I would like to get a number or "Fallen out issues"'s sum remaining per day, which indicates the sum hours of the issues that were part of the export, but no longer is.

Please help me on that!