Nice job creating ddl and sample data.

Unfortunately your data and your description appear to be out of synch with each other. In your desired output table you have loans that don't exist in the #Temp table. If you can explain your situation a little better we can help.

And as a suggestion you should avoid using reserved words like Month as a column name. Not only does it make querying a little more difficult it is totally ambiguous what it means. Same thing with a column named "Flag". What does that mean?