If you want to check for a good data blend, to ensure no missed combinations, place the dimensions you want to join on on the Rows for one source, and the matching dimensions from the other source on the Columns shelf. If you see any headers that are Null, then you know something is missing. Then you can double check by switching the data source order. I would consider this a data quality check, ensuring that the data you are working with is profiled.
The records you are missing probably don't exist on your primary data source. They must exist here for you to see them. Try rebuilding the view and switch the primary and secondary data sources.