Duplicate entries indexer

Hi,

I am trying a formula which finds the duplicate values in one column and indexes it in another column.

What I am trying to do here is tagging a bunch of one duplicate value to lets say 'A', then another bunch of duplicate values should be tagged to 'B' and so on....Is there a way in doing this?

I got the below code in a similar thread in this forum. I tried with some Char data and it worked

=IF(COUNTIF(B$1:B2,B2)>1,VLOOKUP(B2,B$1:C2,2,FALSE),MAX(C$1:C1)+1)


I am trying this with urls, its not working, it assigns value to the first unique url and doesn;t do the same for duplicates one. I am attaching the url file for reference.

In the file I have:
Column A: URL's
Column B: extracted url from A using formula, basically everything that comes after '?' in the url in Column A has been removed and I get the url I wanted.
Column C: Not important
Column D: above formula applied and should display the desired result.

Can someone please tweak this formula to suit URL's

Thanks,
Joseph