Vlookup or Index Match to populate multiple values

Hi..
I am working on a file and trying to match the two columns. But thing is the entries in column 1 and column 2 are not unique. They are repeating, to avoid the confusion, I am taking help of another column containing Index values. Now I am using Index Match to populate the corresponding index value..But I am not getting the results..

vlookup trial.JPG
Here Column 1 has got some values and column 2 has got some values.. I want to match them..For that I am having index value column

Thanks in advance for help..!!

You get your desired result with this formula, but i am not sure if this is what you mean.In E2 and copy down.

Formula:

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Unfortunately iam not able to understand the logic of the expected result. Sorry. Good luck.

I think you need to explain in more detail WHY you want the desired values, with reference to what is in columns A & B.

Hi Glenn. Actually I am trying to match the failure modes and causes of two systems. The idea is that if they match..then I should count number of matches and,if they dont then i need to count the number of failure modes than dont match.. The list of failure modes run into 1000 line items.
Glenn_example.JPG

Please go through the snapshot. For same failure modes...there'll be causes and controls for System A & System B. I want to match the causes..I'll attach the excel file also for your consideration.