First SAVE EVERYTHING!! Then start a new Excel sheet. Copy all the data from Sheet 1, and below it, all the data from Sheet 2. Make sure you have a top row labelled with the titles you just told us. OF course, there will be one more column for Sheet 2. Hit SAVE - give it a title, etc.
Now - you can sort this in a variety of ways. You can choose - but try a few singles - like sorting first by the one that has the most specific data. Too bad there is not DATE, just year. Your 2 sheets will interfile, and you can see duplicates. Try with another sort parameter. After a couple of runs, you should have what you want. I hope this is only a few hundred or less times - if this were THOUSANDS, then yes - you would need a macro. But I have tried to explain this using the easiest method, that will still give you results. Once you find you dupes, you can indicate in another column, the ones that shoudl be deleted. However, SAVE this sheet, paste everything into ANOTHER sheet, and THEN do your deletes. That way, if you find that you took out TOO much - you can go back and retrieve it.
So initially, you will have several sheets or files. Better to be safe than sorry! Once you are dead certain you have done it right, you can always delete the old things. But every DAY, we hear stories here and in the Cell Phones forum, about people that FORGOT to back up. SMART takes seconds - STUPID takes days or longer, and still cannot always be fixed. My late Dad always stressed hard work - but them would say "Why work HARD< when you can work SMART?" - meaning, do it right, and it takes less time and effort - do it WRONG, and hours and hours will be needed.