Merge queries only returning partial information

Thank you for the suggestions and responses, unfortuently these did not resolve our issue, it appeared that when we were merging our data it wasn't importing all of the data even though it was demonstrating a perfect match and all possible causes for difference had been removed, to get around this my manager has completed a significant rebuild on our query as we had it broken up into different steps into smaller query tables. She has worked around the issue and we are back up and running.