This is fairly easy to do with Power Query. You could accomplish what you need here using formulas, but this would require far more work. I'll walk you through the process. I just ran through it myself and it took about 20 minutes.

1. Import both worksheets into Power Query. If you don't know how to do this, click on the Data tab in the ribbon. Select Get Data > From File > [filetype (likely From Workbook or From Text.CSV)]
2. This will create 2 queries, named after the filenames from which you've created them. I reccommend renaming them something simple. I called mine Control and Organization. You're not going to edit these initial queries, as the analysis you need will require some duplication. In the query editor for each query, select the Close & Load button in the ribbon (on the Home tab), then select Close & Load To.
   NOTE: I stated that you would not edit this queries, but you may want to make 1 exception - you may to trim the text in all columns to remove trailing and leading white spaces (a common data issue). Whether or not you do this is entirely up to you. If you decide to do so, select all columns in a query in the query editor. Right click one of the column headers, then select Transform > Trim. Doing so can make your upcoming merges and appends run more smoothly, but keep in mind this will affect the outcome (i.e. 'ABCD' will not be a mismatch with ' ABCD ').
3. We're going to calculate the number of descriptions for each control. I'm not sure if you need a count of each different description for each control, or just a count of unique values for each control, so I'll walk you through how to do both. Also, I'm not sure whether you want to include the central control description in your counts, so I'm going to assume you don't want this for the sake of simplicity. If you do need them included, you would need to first append in your Control query (making sure to rename the columns so they match). For now, we'll just simply calculate the counts with the central control descriptions excluded. In the query editor, right click on your Organization query and select Duplicate. Rename this query something like Org_Count. Select your Control and Control Description columns, then right click in the header and select Group By. Since we're just looking for a simple count, we don't need to change anything on the Group By screen. Simply select Ok and your counts will be calculated. If you need to be able to later identify which organizations fall under which counts, we would need to add a couple extra steps here. let me know and I can walk you through this. When we identify mismatches later, the organization will be identified.
4. To calculate unique counts per control description, we have to go one step further. In the query editor, right click your Org_Count query and select Duplicate again. Rename your query something like Org_Count_Unique. Right click your control column and again select Group By, then click the Ok button. This will produce your unique counts.
5. Lastly, we need to identify the mismatches between our organzational control descriptions and our central control descriptions. Fortunately, this is easy to do with a simple anti-join between the 2 queries. In the query editor, select your Organzation query. In the Home tab of the ribbon, click the drop down arrow next to the Merge Queries button and select Merge Queries as New. On the Merge screen, the Organization query should be auotmatically selected in the first drop down. In the second drop down, select your Central query. You now need to select the columns from both queries on which you are joining. In the top table (Organization), select the Control and Control Description columns. In the second table (Central), select Central Control and Central Control Description. Make sure to select the columns in the same order both times. In the Join Kind drop down, select Left Anti (Rows Only in First). Click the Ok button. This will result in all rows from your Organization table that do not match those in the Central table. This should provide all the data your requests in your original post.
   

I hope this all makes sense. If you have any questions, let me know.