Compare 2 Datasets And Notify If Match Has Not Been Made Then Sumif

Look at the attachment below. I would like to compare two data sets;

DCLG Codes and our internal codes (all highlighted in the colour peach).

One or more of our codes can 'feed into' our parent organizations codes. Please see the Summary sheet and it will become apparent.

At the moment, I have been able to remove the duplicates from the DCLG codes and then 'marry them up' using a SUMIF function to add up all our ledger types- according to their codes.

Basically, the bottom line is that all our spending or income (The ledger Types) has to be grouped (if more than one) and reported back into their system codes.

Here's the more, possibly challenging bit....

Our system generates the ledger types and the monthly spend and year to date every month. from time to time, different ledger types may be added to the table (this will always be from our end).

We would like a way to copy and paste this data next to their table without throwing out the tables or distorting the codes that they relate to on a permanent basis.

My question/s is;

Is there a way to match and validate the data and put in an alert to notify us of the error? And then when we are happy, we could carry on as normal and generate the SUMMARY sheet.

I know of the data validation method and looking for an exact match but I was wondering if the corresponding figures would be affected in anyway.

What may be good would be to have a data dump/input area where the data is matched possibly via a VLOOKUP and anything that is not matched is displayed at the bottom of the list?

The results do not necessarily have to be like what I've suggested above. all I would like to be able to do is match the data first (and their corresponding figures) and output according to their codes. I need to be able to identify new or unmatched Ledger types.

And a report : DCLG Workbook Template Master.xlsx‎