Sequential ABCs fill down

Hello,

I feel like this question is simple, yet so difficult to achieve. Currently, I'm trying to quickly make my controls go from this:

Same name label
Duplicate Label.PNG


to this:

Uniquely labelled control numbers:

Appropriately labelled cells.PNG

As you can see above, it would be adding a, b, c, d, e, etc depending how many of the duplicates there are.

Is there a quick way to achieve this? The tricky part is the many different control numbers, see below:

Tricky part.PNG

I've attached my spreadsheet below so you can have a better example of what I'm trying to ask.

Thank you so much for your time!

When you post a file, it is always a good idea to include your original (existing) data along with your desired results so that we don't have to go through the trouble of typing in the original data or editing your results to produce the original data... we need to try our solutions on your existing data, not your resultant data.

As for your question, put this formula in cell B2 (insert a temporary column if the existing Column B has data) and copy it down to the end of your data...

=A2&IF(A2=A1,CHAR(96+COUNTIF(A$1:A1,A2)),)

then copy Column B and then PasteSpecial Values into Column A, then delete Column B.